Merge mysql.com:/home/kent/bk/tmp/mysql-5.0-build

into  mysql.com:/home/kent/bk/tmp/mysql-5.1-build


BitKeeper/deleted/.del-algor.eps~1a57aff065918206:
  Auto merged
BitKeeper/deleted/.del-dbi.eps~7b1032f98de7736d:
  Auto merged
BitKeeper/deleted/.del-dubois.eps~f24e09a7fa420436:
  Auto merged
BitKeeper/deleted/.del-ecomm.eps~17833026ebd7656:
  Auto merged
BitKeeper/deleted/.del-in_21.eps~8150d06653dab178:
  Auto merged
BitKeeper/deleted/.del-manual.eps~1c2ebcea50b4840c:
  Auto merged
BitKeeper/deleted/.del-msql.eps~f3801b9d166ae4fc:
  Auto merged
BitKeeper/deleted/.del-prof.eps~1f54d9a56eb2b908:
  Auto merged
BitKeeper/deleted/.del-pthreads.eps~2ca8ff2d1181b2c0:
  Auto merged
BitKeeper/deleted/.del-realmen.eps~cc022325d3cb045:
  Auto merged
BitKeeper/deleted/.del-sql-99.eps~f85c06de7a016c7d:
  Auto merged
BitKeeper/deleted/.del-colspec-fix.pl~6c78d3332330b19e:
  Auto merged
BitKeeper/deleted/.del-docbook-fixup.pl~46cf3bdef147084e:
  Auto merged
BitKeeper/deleted/.del-docbook-prefix.pl~876c7d33c68c224a:
  Auto merged
BitKeeper/deleted/.del-docbook-split~be931c3922898d0:
  Auto merged
BitKeeper/deleted/.del-make-docbook~ccac1eb717e92ac9:
  Auto merged
BitKeeper/deleted/.del-make-makefile~39fd454b487126e8:
  Auto merged
BitKeeper/deleted/.del-test-make-manual-de~33cad2886311b8a:
  Auto merged
BitKeeper/deleted/.del-test-make-manual~5da458f958a424ec:
  Auto merged
BitKeeper/deleted/.del-xwf~76b97805d9146b80:
  Auto merged
BitKeeper/deleted/.del-.cvsignore~250f630140b90042:
  Auto merged
BitKeeper/deleted/.del-Tutorial-MySQL-final.txt~6e5b88fe4217504d:
  Auto merged
BitKeeper/deleted/.del-algor.gif~72c40c3bad198f2f:
  Auto merged
BitKeeper/deleted/.del-algor.txt~37d2b5c1290e3cfa:
  Auto merged
BitKeeper/deleted/.del-bk.txt~ffd510fa9531f87c:
  Auto merged
BitKeeper/deleted/.del-dubois.gif~e02d361b13b1c4a4:
  Auto merged
BitKeeper/deleted/.del-dubois.txt~998581cf9040fcc:
  Auto merged
BitKeeper/deleted/.del-ecomm.gif~f9bce6949b171613:
  Auto merged
BitKeeper/deleted/.del-ecomm.txt~27494674104ee9db:
  Auto merged
BitKeeper/deleted/.del-in_21.gif~4a0b14f6d76458a9:
  Auto merged
BitKeeper/deleted/.del-in_21.txt~448fb4b3d8c0b34e:
  Auto merged
BitKeeper/deleted/.del-manual.gif~657cf08119b1b3fc:
  Auto merged
BitKeeper/deleted/.del-manual.txt~4702af61ea5e3c29:
  Auto merged
BitKeeper/deleted/.del-msql.gif~72ea7c6d307b9108:
  Auto merged
BitKeeper/deleted/.del-msql.txt~235ae568824f4073:
  Auto merged
BitKeeper/deleted/.del-mysql-01.gif~6f3f2e474b834ac6:
  Auto merged
BitKeeper/deleted/.del-mysql-02.gif~5e03e2ffa6bd060f:
  Auto merged
BitKeeper/deleted/.del-mysql-03.gif~a510e3599346cd5f:
  Auto merged
BitKeeper/deleted/.del-mysql-04.gif~6c3fdc91da64574:
  Auto merged
BitKeeper/deleted/.del-mysql-05.gif~230c28315136655:
  Auto merged
BitKeeper/deleted/.del-mysql-06.gif~8bb16461fd45634e:
  Auto merged
BitKeeper/deleted/.del-dbi.gif~8f6861147437298b:
  Auto merged
BitKeeper/deleted/.del-dbi.txt~f5cf3fe321168fd5:
  Auto merged
BitKeeper/deleted/.del-mysql-07.gif~b86f918998a2114e:
  Auto merged
BitKeeper/deleted/.del-mysql-08.gif~50fb4d886f82e8bc:
  Auto merged
BitKeeper/deleted/.del-mysql-09.gif~17604ce9d92cd94a:
  Auto merged
BitKeeper/deleted/.del-mysql-10.gif~a8b5306c4d911f8e:
  Auto merged
BitKeeper/deleted/.del-mysql-11.gif~8495404458978524:
  Auto merged
BitKeeper/deleted/.del-mysql-12.gif~18d47c1ad5aef481:
  Auto merged
BitKeeper/deleted/.del-mysql-13.gif~1ad2eedf58da3aaa:
  Auto merged
BitKeeper/deleted/.del-mysql-14.gif~a11e7df8653ad1b1:
  Auto merged
BitKeeper/deleted/.del-mysql-15.gif~64c998fdd6fc1ae1:
  Auto merged
BitKeeper/deleted/.del-mysql-16.gif~6a6c86de2f85f0f5:
  Auto merged
BitKeeper/deleted/.del-mysql-17.gif~b07962578d0952b1:
  Auto merged
BitKeeper/deleted/.del-mysql-compatible.jpg~56ecc684688a7382:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-01.gif~d27d4f0c1a2a6da9:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-02.gif~476224d724007343:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-03.gif~470dd9c9a8bd55fc:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-04.gif~14f429c87c0c718:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-05.gif~e63e7f003b77ad95:
  Auto merged
BitKeeper/deleted/.del-mysql_anim-06.gif~d9cffaf35d9d4719:
  Auto merged
BitKeeper/deleted/.del-prof.gif~2fa8ed201d9d05fe:
  Auto merged
BitKeeper/deleted/.del-prof.txt~9fc04ec3e5ce8361:
  Auto merged
BitKeeper/deleted/.del-pthreads.gif~2d9460dec2577859:
  Auto merged
BitKeeper/deleted/.del-pthreads.txt~fc9e17d021335a39:
  Auto merged
BitKeeper/deleted/.del-realmen.gif~86113e3b1fcbd597:
  Auto merged
BitKeeper/deleted/.del-realmen.txt~81c30565a8f06539:
  Auto merged
BitKeeper/deleted/.del-sql-99.gif~df369376884a5689:
  Auto merged
BitKeeper/deleted/.del-sql-99.txt~eff316adac3dd5b8:
  Auto merged
BitKeeper/deleted/.del-trivial-makeinfo-4.0c.patch~40d336454ecf98db:
  Auto merged

4 files changed, 3 insertions, 1119 deletions

diff --git a/Docs/.cvsignore b/Docs/.cvsignore
index 777efb1eb7b..6a00212535b 100644
--- a/Docs/.cvsignore
+++ b/Docs/.cvsignore
@@ -1,40 +1,5 @@
-COPYING
-COPYING.LIB
+INSTALL-SOURCE
 INSTALL-BINARY
 Makefile
 Makefile.in
-Manual-updates
-before-gpl-changes-manual.texi
-include.texi
-manual-before-gpl.texi
-manual-tmp.aux
-manual-tmp.cp
-manual-tmp.fn
-manual-tmp.ky
-manual-tmp.log
-manual-tmp.pdf
-manual-tmp.pg
-manual-tmp.texi
-manual-tmp.toc
-manual-tmp.tp
-manual-tmp.vr
-manual.aux
-manual.cp
-manual.cps
-manual.fn
-manual.fns
-manual.html
-manual.ky
-manual.log
-manual.pdf
-manual.pg
-manual.toc
-manual.tp
-manual.txt
-manual.vr
-manual_a4.ps
-manual_a4.ps.gz
-manual_letter.ps
-manual_letter.ps.gz
-manual_toc.html
 mysql.info
diff --git a/Docs/linuxthreads.txt b/Docs/linuxthreads.txt
index 30270125c0d..552415fe794 100644
--- a/Docs/linuxthreads.txt
+++ b/Docs/linuxthreads.txt
@@ -1,3 +1,5 @@
+[Note this information is obsolete]
+
 Notes on compiling glibc for the standard MySQL binary:
 
  - make sure you have gcc 2.95 and gmake 3.79 or newer
diff --git a/Docs/my_sys.txt b/Docs/my_sys.txt
deleted file mode 100644
index 85ffc13ecb4..00000000000
--- a/Docs/my_sys.txt
+++ /dev/null
@@ -1,140 +0,0 @@
-Functions i mysys: (For flags se my_sys.h)
-
- int my_copy _A((const char *from,const char *to,myf MyFlags));
-	- Copy file
-
- int my_delete _A((const char *name,myf MyFlags));
-	- Delete file
-
- int my_getwd _A((string buf,uint size,myf MyFlags));
- int my_setwd _A((const char *dir,myf MyFlags));
-	- Get and set working directory
-
- string my_tempnam _A((const char *pfx,myf MyFlags));
-	- Make a uniq temp file name by using dir and adding something after
-	 pfx to make name uniq. Name is made by adding a uniq 6 length-string
-	 and TMP_EXT after pfx.
-	 Returns pointer to malloced area for filename. Should be freed by
-	 free().
-
- File my_open _A((const char *FileName,int Flags,myf MyFlags));
- File my_create _A((const char *FileName,int CreateFlags,
-			  int AccsesFlags, myf MyFlags));
- int my_close _A((File Filedes,myf MyFlags));
- uint my_read _A((File Filedes,byte *Buffer,uint Count,myf MyFlags));
- uint my_write _A((File Filedes,const byte *Buffer,uint Count,
-			 myf MyFlags));
- ulong my_seek _A((File fd,ulong pos,int whence,myf MyFlags));
- ulong my_tell _A((File fd,myf MyFlags));
-	- Use instead of open,open-with-create-flag, close read and write
-	  to get automatic error-messages (flag: MYF_WME) and only have
-	  to test for != 0 if error (flag: MY_NABP).
-
- int my_rename _A((const char *from,const char *to,myf MyFlags));
-	- Rename file
-
- FILE *my_fopen _A((const char *FileName,int Flags,myf MyFlags));
- FILE *my_fdopen _A((File Filedes,int Flags,myf MyFlags));
- int my_fclose _A((FILE *fd,myf MyFlags));
- uint my_fread _A((FILE *stream,byte *Buffer,uint Count,myf MyFlags));
- uint my_fwrite _A((FILE *stream,const byte *Buffer,uint Count,
-			  myf MyFlags));
- ulong my_fseek _A((FILE *stream,ulong pos,int whence,myf MyFlags));
- ulong my_ftell _A((FILE *stream,myf MyFlags));
-	- Same read-interface for streams as for files
-
- gptr _mymalloc _A((uint uSize,const char *sFile,
-			  uint uLine, myf MyFlag));
- gptr _myrealloc _A((string pPtr,uint uSize,const char *sFile,
-			   uint uLine, myf MyFlag));
- void _myfree _A((gptr pPtr,const char *sFile,uint uLine));
- int _sanity _A((const char *sFile,unsigned int uLine));
- gptr _myget_copy_of_memory _A((const byte *from,uint length,
-				      const char *sFile, uint uLine,
-				      myf MyFlag));
-	- malloc(size,myflag) is mapped to this functions if not compiled
-	  with -DSAFEMALLOC
-
- void TERMINATE _A((void));
-	- Writes malloc-info on stdout if compiled with -DSAFEMALLOC.
-
- int my_chsize _A((File fd,ulong newlength,myf MyFlags));
-	- Change size of file
-
- void my_error _D((int nr,myf MyFlags, ...));
-	- Writes message using error number (se mysys/errors.h) on
-	  stdout or curses if  MYSYS_PROGRAM_USES_CURSES() is called.
-
- void my_message _A((const char *str,myf MyFlags));
-	- Writes message-string on
-	 stdout or curses if  MYSYS_PROGRAM_USES_CURSES() is called.
-
- void my_init _A((void ));
-	- Start each program (in main) with this.
- void my_end _A((int infoflag));
-	- Gives info about program.
-	- If infoflag & MY_CHECK_ERROR prints if some files are left open
-	- If infoflag & MY_GIVE_INFO   prints timing info and malloc info
-	  about prog.
-
- int my_redel _A((const char *from, const char *to, int MyFlags));
-	- Delete from before rename of to to from. Copyes state from old
-	  file to new file. If MY_COPY_TIME is set sets old time.
-
- int my_copystat _A((const char *from, const char *to, int MyFlags));
-	- Copye state from old file to new file.
-	  If MY_COPY_TIME is set sets copy also time.
-
- string my_filename _A((File fd));
-	- Give filename of open file.
-
- int dirname _A((string to,const char *name));
-	- Copy name of directory from filename.
-
- int test_if_hard_path _A((const char *dir_name));
-	- Test if dirname is a hard path (Starts from root)
-
- void convert_dirname _A((string name));
-	- Convert dirname acording to system.
-	  - In MSDOS changes all caracters to capitals and changes '/' to
-	    '\'
- string fn_ext _A((const char *name));
-	- Returns pointer to extension in filename
- string fn_format _A((string to,const char *name,const char *dsk,
-			    const char *form,int flag));
-	format a filename with replace of library and extension and
-	converts between different systems.
-	params to and name may be identicall
-	function dosn't change name if name != to
-	Flag may be:	1   force replace filnames library with 'dsk'
-			2   force replace extension with 'form' */
-			4   force Unpack filename (replace ~ with home)
-			8   Pack filename as short as possibly for output to
-			    user.
-	All open requests should allways use at least:
-	"open(fn_format(temp_buffe,name,"","",4),...)" to unpack home and
-	convert filename to system-form.
-
- string fn_same _A((string toname,const char *name,int flag));
-	- Copys directory and extension from name to toname if neaded.
-	  copy can be forced by same flags that in fn_format.
-
- int wild_compare _A((const char *str,const char *wildstr));
-	- Compare if str matches wildstr. Wildstr can contain "*" and "?"
-	  as match-characters.
-	  Returns 0 if match.
-
- void get_date _A((string to,int timeflag));
-	- Get current date in a form ready for printing.
-
- void soundex _A((string out_pntr, string in_pntr))
-	- Makes in_pntr to a 5 chars long string. All words that sounds
-	  alike have the same string.
-
- int init_key_cache _A((ulong use_mem,ulong leave_this_much_mem));
-	- Use cacheing of keys in MISAM, PISAM, and ISAM.
-	  KEY_CACHE_SIZE is a good size.
-	  - Remember to lock databases for optimal cacheing
-
- void end_key_cache _A((void));
-	- End key-cacheing.
diff --git a/Docs/net_doc.txt b/Docs/net_doc.txt
deleted file mode 100644
index 4f21383c06d..00000000000
--- a/Docs/net_doc.txt
+++ /dev/null
@@ -1,943 +0,0 @@
- MySQL Client/Server Protocol Documentation
-
-
-
-Introduction
-------------
-
-
-This paper has the objective of presenting a through description
-of the client/server protocol that is embodied in MySQL. Particularly,
-this paper aims to document and describe:
-
-- manner in which MySQL server detects client connection requests and
-  creates connection
-- manner in which MySQL client C API call connects to server - the
-  entire protocol of sending/receiving data by MySQL server and C API
-  code
-- manner in which queries are sent by client C API calls to server
-- manner in which query results are sent by server
-- manner in which query results are resolved by server
-- sending and receiving of error messages
-
-
-This paper does not have the goal or describing nor documenting other
-related MySQL issues, like usage of thread libraries, MySQL standard
-library set, MySQL strings library and other MySQL specific libraries,
-type definitions and utilities.
-
-Issues that are covered by this paper are contained in the following
-source code files:
-
-- libmysql/net.c and sql/net_serv.cc, the two being identical
-- client/libmysql.c (not entire file is covered)
-- include/mysql_com.h
-- include/mysql.h
-- sql/mysqld.cc (not entire file is covered)
-- sql/net_pkg.cc
-- sql/sql_base.cc (not entire file is covered)
-- sql/sql_select.cc (not entire file is covered)
-- sql/sql_parse.cc (not entire file is covered)
-
-Note: libmysql/net.c was client/net.c prior to MySQL 3.23.11.
-sql/net_serv.cc was sql/net_serv.c prior to MySQL 3.23.16.
-
-Beside this introduction this paper presents basic definitions,
-constants, structures and global variables, all related functions in
-server and in C API. Textual description of the entire protocol
-functioning is described in the last chapter of this paper.
-
-
-Constants, structures and global variables
-------------------------------------------
-
-This chapter will describe all constants, structures and
-global variables relevant to client/server protocol.
-
-Constants
-
-They are important as they contain default values, the ones
-that are valid if options are not set in any other way. Beside that
-MySQL source code does not contain a single non-defined constant in
-its code. This description of constants does not include
-configuration and conditional compilation #defines.
-
-NAME_LEN          - field and table name length, current value 64
-HOSTNAME_LENGTH   - length of the hostname, current value 64
-USERNAME_LENGTH   - username length, current value 16
-MYSQL_PORT        - default TCP/IP port number, current value 3306
-MYSQL_UNIX_ADDR   - full path of the default Unix socket file, current value
-                    "/tmp/mysql.sock"
-MYSQL_NAMEDPIPE   - full path of the default NT pipe file, current value
-                    "MySQL"
-MYSQL_SERVICENAME - name of the MySQL Service on NT, current value "MySQL"
-NET_HEADER_SIZE   - size of the network header, when no
-                    compression is used, current value 4
-COMP_HEADER_SIZE - additional size of network header when
-                    compression is used, current value 3
-
-What follows are set of constants, defined in source only, which
-define capabilities of the client built with that version of C
-API. Simply, when some new feature is added in client, that client
-feature is defined, so that server can detect what capabilities a
-client program has.
-
-CLIENT_LONG_PASSWORD    - client supports new more secure passwords
-CLIENT_LONG_FLAG        - client uses longer flags
-CLIENT_CONNECT_WITH_DB  - client can specify db on connect
-CLIENT_COMPRESS         - client can use compression protocol
-CLIENT_ODBC             - ODBC client
-CLIENT_LOCAL_FILES      - client can use LOAD DATA INFILE LOCAL
-CLIENT_IGNORE_SPACE     - client can ignore spaces before '('
-CLIENT_CHANGE_USER      - client supports the mysql_change_user()
-
-What follows are other constants, pertaining to timeouts and sizes
-
-MYSQL_ERRMSG_SIZE       - maximum size of error message string, current value 200
-NET_READ_TIMEOUT        - read timeout, current value 30 seconds
-NET_WRITE_TIMEOUT       - write timeout, current value 60 seconds
-NET_WAIT_TIMEOUT        - wait for new query timeout, current value 8*60*60
-                          seconds, that is, 8 hours
-packet_error            - value returned in case of socket errors, current
-                          value -1
-TES_BLOCKING            - used in debug mode for setting up blocking testing
-RETRY COUNT             - number of times network read and write will be
-                          retried, current value 1
-
-There are also error messages for last_errno, which depict system
-errors, and are used on the server only.
-
-ER_NET_PACKAGE_TOO_LARGE  - packet is larger than max_allowed_packet
-ER_OUT_OF_RESOURCES       - practically no more memory
-ER_NET_ERROR_ON_WRITE     - error in writing to NT Named Pipe
-ER_NET_WRITE_INTERRUPTED  - some signal or interrupt happened
-                            during write
-ER_NET_READ_ERROR_FROM_PIPE - error in reading from NT Named Pipe
-ER_NET_FCNTL_ERROR        - error in trying to set fcntl on socket
-                            descriptor
-ER_NET_PACKETS_OUT_OF_ORDER - packet numbers on client and
-                              server side differ
-ER_NET_UNCOMPRESS_ERROR   - error in uncompress of compressed packet
-
-
-                Structs and enums
-
-
-struct NET
-
-This is MySQL's network handle structure, used in all client/server
-read/write functions. On the server, it is initialized and preserved
-in each thread. On the client, it is a part of the MYSQL struct,
-which is the MySQL handle used in all C API functions. This structure
-uniquely identifies a connection, either on the server or client
-side.  It consists of the following fields:
-
-    Vio* vio - explained above
-    HANDLE hPipe - Handle for NT Named Pipe file
-    my_socket fd - file descriptor used for both TCP/IP socket and
-                   Unix socket file
-    int fcntl - contains info on fcntl options used on fd. Mostly
-                used for saving info if blocking is used or not
-    unsigned char *buff - network buffer used for storing data for
-                          reading from/writing to socket
-    unsigned char,*buff_end - points to the end of buff
-    unsigned char *write_pos - present writing position in buff
-    unsigned char *read_pos - present reading position in buff. This
-                              pointer is used for reading data after
-                              calling my_net_read function and function
-                              that are just its wrappers
-    char last_error[MYSQL_ERRMSG_SIZE] - holds last error message
-    unsigned int last_errno - holds last error code of the network
-                              protocol. Its possible values are listed
-                              in above constants. It is used only on
-                              the server side
-    unsigned int max_packet - holds current value of buff size
-    unsigned int timeout - stores read timeout value for that connection
-    unsigned int pkt_nr - stores the value of the current packet number in
-                          a batch of packets. Used primarily for
-                          detection of protocol errors resulting in a
-                          mismatch
-    my_bool error - holds either 1 or 0 depending on the error condition
-    my_bool return_errno - if its value != 0 then there is an error in
-                           protocol mismatch between client and server
-    my_bool compress - if true compression is used in the protocol
-    unsigned long remain_in_buf - used only in reading compressed packets.
-                                  Explained in my_net_read
-    unsigned long length - used only for storing the length of the read
-                           packet. Explained in my_net_read
-    unsigned long buf_length - used only in reading compressed packets.
-                               Explained in my_net_read
-    unsigned long where_b - used only in reading compressed packets.
-                            Explained in my_net_read
-    short int more - used for reporting in mysql_list_processes
-    char save_char - used in reading compressed packets for saving chars
-                     in order to make zero-delimited strings. Explained
-                     in my_net_read
-
-A few typedefs will be defined for easier understanding of the text that
-follows.
-
-typedef char **MYSQL_ROW - data containing one row of values
-
-typedef unsigned int MYSQL_FIELD_OFFSET - offset in bytes of the current field
-
-typedef MYSQL_ROWS *MYSQL_ROW_OFFSET - offset in bytes of the current row
-
-struct MYSQL_FIELD - contains all info on the attributes of a
-specific column in a result set, plus info on lengths of the column in
-a result set. This struct is tagged as st_mysql_field. This structure
-consists of the following fields:
-
-    char *name - name of column
-    char *table - table of column if column was a field and not
-                  an expression or constant
-    char *def - default value (set by mysql_list_fields)
-    enum enum_field_types type - see above
-    unsigned int length - width of column in the current row
-    unsigned int max_length - maximum width of that column in entire
-                              result set
-    unsigned int flags - corresponding to Extra in DESCRIBE
-    unsigned int decimals - number of decimals in field
-
-
-struct MYSQL_ROWS - a node for each row in the single linked
-list forming entire result set. This struct is tagged as
-st_mysql_rows, and has two fields:
-
-    struct st_mysql_rows *next - pointer to the next one
-    MYSQL_ROW data - see above
-
-
-struct MYSQL_DATA - contains all rows from result set. It is
-tagged as st_mysql_data and has following fields:
-
-    my_ulonglong rows - how many rows
-    unsigned int fields - how many columns
-    MYSQL_ROWS *data - see above. This is the first node of the linked list
-    MEM_ROOT alloc - MEM_ROOT is MySQL memory allocation structure, and
-                     this field is used to store all fields and rows.
-
-
-struct st_mysql_options - holds various client options, and
-contains following fields:
-
-    unsigned int connect_timeout - time in seconds for connection
-    unsigned int client_flag - used to hold client capabilities
-    my_bool compress - boolean for compression
-    my_bool named_pipe - is Named Pipe used? (on NT)
-    unsigned int port - what TCP port is used
-    char *host - host to connect to
-    char *init_command - command to be executed upon connection
-    char *user - account name on MySQL server
-    char *password - password for the above
-    char *unix_socket - full path for Unix socket file
-    char *db - default database
-    char *my_cnf_file - optional configuration file
-    char *my_cnf_group - optional header for options
-
-
-struct MYSQL - MySQL client's handle. Required for any
-operation issued from client to server. Tagged as st_mysql and having
-following fields:
-
-    NET net - see above
-    char *host - host on which MySQL server is running
-    char *user - MySQL username
-    char *passwd - password for above
-    char *unix_socket- full path of Unix socket file
-    char *server_version - version of the server
-    char *host_info - contains info on how has connection been
-                      established, TCP port, socket or Named Pipe
-    char *info - used to store information on the query results,
-                 like number of rows affected etc.
-    char *db - current database
-    unsigned int port - TCP port in use
-    unsigned int client_flag - client capabilities
-    unsigned int server_capabilities - server capabilities
-    unsigned int protocol_version - version of the protocol
-    unsigned int field_count - used for storing number of fields
-                               immediately upon execution of a query,
-                               but before fetching rows
-    unsigned long thread_id - server thread to which this connection
-                              is attached
-    my_ulonglong affected_rows - used for storing number of rows
-                                 immediately upon execution of a query,
-                                 but before fetching rows
-    my_ulonglong insert_id - fetching LAST_INSERT_ID() through client C API
-    my_ulonglong extra_info - used by mysqlshow
-unsigned long packet_length - saving size of the first packet upon
-                              execution of a query
-    enum mysql_status status - see above
-    MYSQL_FIELD *fields - see above
-    MEM_ROOT field_alloc - memory used for storing previous field (fields)
-    my_bool free_me - boolean that flags if MYSQL was allocated in mysql_init
-    my_bool reconnect - used to automatically reconnect
-    struct st_mysql_options options - see above
-    char scramble_buff[9] - key for scrambling password before sending it
-                           to server
-
-
-struct MYSQL_RES - tagged as st_mysql_res and used to store
-entire result set from a single query. Contains following fields:
-
-    my_ulonglong row_count - number of rows
-    unsigned int field_count - number of columns
-    unsigned int current_field - cursor for fetching fields
-    MYSQL_FIELD *fields - see above
-    MYSQL_DATA *data - see above, and used in buffered reads, that is,
-                       mysql_store_result only
-    MYSQL_ROWS *data_cursor - pointing to the field of above "data"
-    MEM_ROOT field_alloc - memory allocation for above "fields"
-    MYSQL_ROW row - used for storing row by row in unbuffered reads,
-                    that is, in mysql_use_result
-    MYSQL_ROW current_row - cursor to the current row for buffered reads
-    unsigned long *lengths - column lengths of current row
-    MYSQL *handle - see above, used in unbuffered reads, that is, in
-                    mysql_use_result
-    my_bool eof - used by mysql_fetch_row as a marker for end of data
-
-
-
-                                Global variables
-
-
-unsigned long max_allowed_packet - maximum allowable value of network
-                                   buffer. Default value - 1MB
-
-unsigned long net_buffer_length - default, starting value of network
-                                  buffer - 8KB
-
-unsigned long bytes_sent - total number of bytes written since startup
-                           of the server
-
-unsigned long bytes_received - total number of bytes read since startup
-                               of the server
-
-
-Synopsis of the basic client/server protocol
---------------------------------------------
-
-Purpose of this chapter is to provide a complete picture of
-the basic client/server protocol implemented in MySQL. It was felt
-it is necessary after writing descriptions for all of the functions
-involved in basic protocol. There are at present 11 functions
-involved, with several structures, many constants etc, which are all
-described in detail. But as a forest could not be seen from the trees,
-so the concept of the protocol could not be deciphered easily from a
-thorough documentation of minutiae.
-
-Although the concept of the protocol was not changed with the
-introduction of vio system, embodied in violate.cc source file and VIO
-system, the introduction of these has changed the code substantially. Before
-VIO was introduced, functions for reading from/writing to network
-connection had to deal with various network standards. So, these functions
-depended on whether TCP port or Unix socket file or NT Named Pipe file is
-used. This is all changed now and single vio_ functions are called, while
-all this diversity is covered by vio_ functions.
-
-In MySQL a specific buffered network input/output transport model
-has been implemented. Although each operating system may have its
-own buffering for network connections, MySQL has added its own
-buffering model. This same for each of the three transport protocol
-types that are used in MySQL client/server communications, which
-are TCP/IP sockets (on all systems), Unix socket files on Unix and
-Unix-like operating systems and Named Pipe files on NT. Although
-TCP/IP sockets are omnipresent, the latter two types have been added
-for local connections. Those two connection types can be used in
-local mode only, that is, when both client and server reside on the
-same host, and are introduced because they enable better speeds for
-local connections. This is especially useful for WWW type of
-applications. Startup options of MySQL server allow that either
-TCP/IP sockets or local connection (OS dependent) can be disallowed.
-
-In order to implement buffered input/output, MySQL allocates a
-buffer. The starting size of this buffer is determined by the value
-of the global variable net_buffer_length, which can be changed at
-MySQL server startup. This is, as explained, only the startup length
-of MySQL network buffer. Because a single item that has to be read
-or written can be larger than that value, MySQL will increase buffer
-size as long as that size reaches value of the global variable
-max_allowed_packet, which is also settable at server startup. Maximum
-value of this variable is limited by the way MySQL stores/reads
-sizes of packets to be sent/read, which means by the way MySQL
-formats packages.
-
-Basically each packet consists of two parts, a header and data. In
-the case when compression is not used, header consists of 4 bytes
-of which 3 contain the length of the packet to be sent and one holds
-the packet number. When compression is used there are onother 3
-bytes which store the size of uncompressed data. Because of the way
-MySQL packs length into 3 bytes, plus due to the usage of some
-special values in the most significant byte, maximum size of
-max_allowed_packet is limited to 24MB at present. So, if compression
-is not used, at first 4 bytes are written to the buffer and then
-data itself. As MySQL buffers I/O logical packets are packet together
-until packets fill up entire size of the buffer. That size no less
-than net_buffer_size, but no greater than max_allowed_packet. So,
-actual writing to the network is done when this buffer is filled
-up. As frequently sequence of buffers make a logical unit, like a
-result set, then at the end of sending data, even if buffer is not
-full, data is written (flushed to the connection) with a call of
-the net_flush function. So that no single packet can be larger than
-this value, checks are made throughout the code to make sure that
-no single field or command could exceed that value.
-
-In order to maintain coherency in consecutive packets, each packet
-is numbered and their number stored as a part of a header, as
-explained above. Packets start with 0, so whenever a logical packet
-is written, that number is incremented. On the other side when
-packets are read, value that is fetched is compared with the value
-stored and if there is no mismatch that value is incremented, too.
-Packet number is reset on the client side when unwanted connections
-are removed from the connection and on the server side when a new
-command has been started.
-
-
-So, before writing, the buffer contains a sequence of logical
-packets, consisting of header plus data consecutively. If compression
-is used, packet numbers are not stored in each header of the logical
-packets, but a whole buffer, or a part of it if flushing is done,
-containing one or more logical packets are compressed. In that case
-a new larger header, is formed, and all logical packets contained
-in the buffer are compressed together. This way only one packet is
-formed which makes several logical packets, which improves both
-speed and compression ratio. On the other side, when this large
-compressed packet is read, it is first uncompressed, and then logical
-packets are sent, one by one, to the calling functions.
-
-
-All this functionality is described in detail in the following
-chapter. It does not contain functions that form logical packets, or
-that read and write to connections but also functions that are used
-for initialization, clearing of connections. There are functions at
-higher level dealing with sending fields, rows, establishing
-connections, sending commands, but those are not explained in the
-following chapter.
-
-
-Functions utilized in client/server protocol
---------------------------------------------
-
-First of all, functions are described that are involved in preparing,
-reading, or writing data over TCP port, Unix socket file, or named
-pipe, and functions directly related to those. All of these functions
-are used both in server and client. Server and client specific code
-segments are documented in each function description.
-
-Each MySQL function checks for errors in memory allocation and
-freeing, as well as in every OS call, like the one dealing with
-files and sockets, and for errors in indigenous MySQL function
-calls. This is expected, but has to be said here so as not to repeat
-it in every function description.
-
-Older versions of MySQL have utilized the following macros for
-reading from or writing to a socket.
-
-raw_net_read - calls OS function recv function that reads N bytes
-from a socket into a buffer. Number of bytes read is returned.
-
-raw_net_write - calls OS function send to write N bytes from a
-buffer to socket. Number of bytes written is returned.
-
-These macros are replaced with VIO (Virtual I/O) functions.
-
-
-Function name: my_net_init
-
-Parameters: struct NET *, enum_net_type, struct Vio
-
-Return value: 1 for error, 0 for success
-
-Function purpose: To initialize properly all NET fields,
-                  allocate memory and set socket options
-
-Function description
-
-First of all, buff field of NET struct is allocated to the size of
-net_buffer_length, and on failure function exits with 0. All fields
-in NET are set to their default or starting values. As net_buffer_length
-and max_allowed_packet are configurable, max_allowed_packet is set
-equal to net_buffer_length if the latter one is greater. max_packet
-is set for that NET to net_buffer_length, and buff_end points to
-buff end. vio field is set to the second parameter.  If it is a
-real connection, which is the case when second parameter is not
-null, then fd field is set by calling vio_fd function. read_pos and
-write_pos to buff, while remaining integers are set to 0. If function
-is run on the MySQL server on Unix and server is started in a test
-mode that would require testing of blocking, then vio_blocking
-function is called. Last, fast throughput mode is set by a call to
-vio_fastsend function.
-
-
-Function name: net_end
-
-Parameters: struct NET *
-
-Return value: void
-
-Function purpose: To release memory allocated to buff
-
-
-
-Function name: net_realloc (private, static function)
-
-Parameters: struct NET, ulong (unsigned long)
-
-Return value: 1 for error, 0 for success
-
-Function purpose: To change memory allocated to buff
-
-Function description
-
-New length of buff field of NET struct is passed as second parameter.
-It is first checked versus max_allowed_packet and if greater, an
-error is returned. New length is aligned to 4096-byte boundary. Then,
-buff is reallocated, buff_end, max_packet, and write_pas reset to
-the same values as in my_net_init.
-
-
-
-Function name: net_clear (used on client side only)
-
-Parameters: struct NET *
-
-Return value: void
-
-Function purpose: To read unread packets
-
-Function description
-
-This function is used on client side only, and is executed
-only if a program is not started in test mode. This function reads
-unread packets without processing them. First, non-blocking mode is
-set on systems that do not have non-blocking mode defined. This is
-performed by checking the mode with vio_is_blocking function. and
-setting non-blocking mode by vio_blocking function. If this operation
-was successful, then packets are read by vio_read function, to which
-vio field of NET is passed together with buff and max_packet field
-values. field of the same struct at a length of max_packet. If
-blocking was active before reading is performed, blocking is set with
-vio_blocking function. After reading has been performed, pkt_nr is
-reset to 0 and write_pos reset to buff. In order to clarify some
-matters non-blocking mode enables executing program to dissociate from
-a connection, so that error in connection would not hang entire
-program or its thread.
-
-Function name: net_flush
-
-Parameters: struct NET *
-
-Return value: 1 for error, 0 for success
-
-Function purpose: To write remaining bytes in buff to socket
-
-Function description
-
-net_real_write (described below) is performed is write_pos
-differs from buff, both being fields of the only parameter. write_pos
-is reset to buff. This function has to be used, as MySQL uses buffered
-writes (as will be explained more in the function net_write_buff).
-
-
-Function name: my_net_write
-
-Parameters: struct NET *, const char *, ulong
-
-Return value: 1 for error, 0 for success
-
-Function purpose: Write a logical packet in the second parameter
-                  of third parameter length
-
-Function description
-
-The purpose of this function is to prepare a logical packet such
-that entire content of data, pointed to by second parameter and in
-length of third parameter is sent to the other side. In case of
-server, it is used for sending result sets, and in case of client
-it is used for sending local data. This function foremost prepares
-a header for the packet. Normally, the header consists of 4 bytes,
-of which the first 3 bytes contain the length of the packet, thereby
-limiting a maximum allowable length of a packet to 16MB, while the
-fourth byte contains the packet number, which is used when one large
-packet has to be divided into sequence of packets. This way each
-sub-packet gets its number which should be matched on the other
-side. When compression is used another three bytes are added to
-packet header, thus packet header is in that case increased to 7
-bytes. Additional three bytes are used to save the length of
-compressed data. As in connection that uses compression option,
-code packs packets together,, a header prepared by this function
-is later not used in writing to / reading from network, but only
-to distinguish logical packets within a buffered read operation.
-
-
-This function, first stores the value of the third parameter into the
-first 3 bytes of local char variable of NET_HEADER_SIZE size by usage
-of function int3store. Then, at this point, if compression is not
-used, pkt_nr is increased, and its value stored in the last byte of
-the said local char[] variable. If compression is used, 0 is stored in
-both values. Then those four bytes are sent to other side by the usage
-of the function net_write_buff(to be explained later on), and if
-successful, entire packet in second parameter of the length described
-in third parameter is sent by the usage of the same function.
-
-
-Function name: net_write_command
-
-Parameters: struct NET *, char, const char *, ulong
-
-Return value: 1 for error, 0 for success
-
-Function purpose: Send a command with a packet as in previous function
-
-Function description
-
-This function is very similar to the previous one. The only
-difference is that first packet is enlarged by one byte, so that the
-command precedes the packet to be sent. This is implemented by
-increasing first packet by one byte, which contains a command code. As
-command codes do not use the range of values that are used by character
-sets, so when the other side receives a packet, first byte after
-header contains a command code. This function is used by client for
-sending all commands and queries, and by server in connection process
-and for sending errors.
-
-
-Function name: net_write_buff (private, static function)
-
-Parameters: struct NET *, const char *, uint
-
-Return value: 1 for error, 0 for success
-
-Function purpose: To write a packet of any size by cutting it
-and using next function for writing it
-
-Function description
-
-This function was created after compression feature has been
-added to MySQL. This function supposes that packets have already been
-properly formatted, regarding packet header etc. The principal reason for
-this function to exist is because a packet that is sent by client or
-server does not have to be less than max_packet. So this function
-first calculates how much data has been left in a buff, by getting a
-difference between buff_end and write_pos and storing it to local
-variable left_length. Then a loop is run as long as the length to be
-sent is greater than length of left bytes (left_length). In a loop
-data from second parameter is copied to buff at write_pos, as much as
-it can be, that is, by left_length. Then net_real_write function is called
-(see below) with NET, buff, and max_packet parameters. This function
-is the lowest level function that writes data over established
-connection. In the loop, write_pos is reset to buff, the pointer to data
-(second parameter) is moved by the amount of data sent (left_length),
-length of data to be sent (third parameter) is decreased by the amount
-sent (left_length) and left_length is reset to max_packet value, which
-ends the loop. This logic was necessary, as there could have been some
-data yet unsent (write_pos != buf), while data to be sent could be as
-large as necessary, thus requiring many loops. At the end of function,
-remaining data in second parameter are copied to buff at write_pos, by
-the remaining length of data to be sent (third parameter). So, in the
-next call of this function remaining data will be sent, as buff is
-used in the call to net_real_write. It is very important to note that if
-a packet to be sent is less than the number of bytes that are still
-available in buff, then there will be no writing over network, but
-only logical packets will be added one after another. This will
-accelerate network traffic, plus if compression is used, the
-expected compression rate would be higher. That is why server or
-client functions that sends data uses at the end of data net_flush
-function described above.
-
-
-Function name: net_real_write
-
-Parameters: struct NET *, const char *, ulong
-
-Return value: 1 for error, 0 for success
-
-Function purpose: To write data to a socket or pipe, with
-compression if used
-
-Function description
-
-First, more field is set to 2, to enable reporting in
-mysql_list_processes. Then if compression is enabled on that
-connection, a new local buffer (variable b) is initialized to the
-length of total header (normal header + compression header) and if no
-memory is available, an error is returned. This buffer (b) is used for
-holding the final, compressed packet to be written over the
-connection. Furthermore in compression initialization, second
-parameter at length of third parameter is copied to the local buffer
-b, and MySQL's wrapped zlib's compression function is run at total
-header offset of the local buffer. Please, do note that this function
-does not test effectiveness of compression. If compression is turned
-on in some connection, it is used all of the time. Also, it is very
-important to be cognizant of the fact that this algorithm makes
-possible that a single compressed packet contains several logical
-packets. In this way compression rate is increased and network
-throughput is increased as well. However, this algorithm has
-consequences on the other side, that reads compressed packet, which
-is covered in my_net_read function. After compression is done, the full
-compression header is properly formed with the packet number,
-compressed and uncompressed lengths. At the end of compression code,
-third parameter is increased by total header length, as the original
-header is not used (see above), and second parameter, pointer to data,
-is set to point to local buffer b, in order that the further flow of
-function is independent of compression. If a function is executed
-on server side, a thread alarm initialized and if non-blocking is
-active set at NET_WRITE_TIMEOUT. Two local (char *) pointers are
-initialized, pos at beginning of second parameter, and end at end of
-data. Then the loop is run as long as all data is written, which means
-as long as pos != end. First vio_write function is called, with
-parameters of vio field, pos and size of data (end - pos). Number of
-bytes written over connection is saved in local variable (length). If
-error is returned local bool variable (interrupted) is set according
-to the return value of the vio_should_retry called with vio field as
-parameter. This bool variable indicates whether writing was
-interrupted in some way or not.
-
-Further, error from vio_write is treated differently on Unix versus
-other OS's (Win32 or OS/2). On Unix an alarm is set if one is not
-in use, no bytes have been written and there has been no interruption.
-Also, in that case, if connection is not in blocking mode, a sub-loop
-is run as long as blocking is not set with vio_blocking function.
-Within the loop another run of above vio_write is run based on
-return value of vio_is_retry function, provided number of repeated
-writes is less than RETRY_COUNT. If that is not the case, error
-field of struct NET is set to 1 and function exits. At the exit
-of sub-loop number of reruns already executed is reset to zero and
-another run of above vio_write function is attempted. If the function
-is run on Win32 and OS/2, and in the case that function flow was
-not interrupted and thread alarm is not in use, again the main loop
-is continued until pos != end. In the case that this function is
-executed on thread safe client program, a communication flow is
-tested on EINTR, caused by context switching, by use of vio_errno
-function, in which case the loop is continued. At the end of
-processing of the error from vio_write, error field of struct NET
-is set, and if on server last_errno field is set to
-ER_NET_WRITE_INTERRUPTED in the case that local bool variable
-(interrupted) is true or to ER_NET_ERROR_ON_WRITE. Before the end
-of loop, in order to make possible evaluation of the loop condition,
-pos is increased by the value written in last iteration (length).
-Also global variable bytes_sent is increased by the same value, for
-status purposes. At the end of the functions more fields is reset,
-in case of compression, compression buffer (b) memory is released
-and if thread is still in use, it is ended and blocking state is
-reset to its original state, and function returns error is all bytes
-are not written.
-
-
-
-Function name: my_real_read (private, static function)
-
-Parameters: struct NET *, ulong *
-
-Return value: length of bytes read
-
-Function purpose: low level network connection read function
-
-Function description
-
-This function has made as a separate one when compression was
-introduced in MySQL client/server protocol . It contains basic, low
-level network reading functionality, while all dealings with
-compressed packets are handled in next function. Compression in this
-function is only handled in as much to unfold the length of uncompressed
-data. First blocking state of connection is saved in local bool
-variable net_blocking, and field more is set 1 for detailed reporting
-in mysqld_list_processes. A new thread alarm is initialized, in order
-to enable read timeout handling, and if on server and a connection can
-block a program, the alarm is set at a value of timeout field. Local
-pointer is set to the position of the next logical packet, with its
-header skipped, which is at field where_b offset from buff. Next, a
-two time run code is entered. A loop is run exactly two times because
-first time number of bytes to be fetched (remain) are set to the
-header size, which is different when compression is used or not used
-on the connection. After first fetch has been done, number of packets
-that will be received in second iteration is well known, as fetched
-header contains the size of packet, packet number, and in the case of
-compression, the size of the uncompressed packet. Then, as long as there are
-bytes to read the loop is entered with first reading data from network
-connection with vio_read function, called with parameters of field
-vio, current position and remaining number of bytes, which value is
-hold by local variable (remain) initialized at the value of header size,
-which differs if compression is used. Number of bytes read are
-returned in local length variable. If error is returned local bool
-variable (interrupted) is set according to the return value of the
-vio_should_retry called with vio field as parameter. This bool
-variable indicates whether reading was interrupted in some way or not.
-
-Further, error from vio_read is treated differently on Unix versus
-other OS's (Win32 or OS/2). On Unix an alarm is set if one is not
-in use, no bytes have been read and there has been no interruption.
-Also, in that case, if connection is not in blocking mode, a sub-loop
-is run as long as blocking is not set with vio_blocking function.
-Within the loop another run of above vio_read is run based on return
-value of vio_is_retry function, provided number of repeated writes
-is less than RETRY_COUNT. If that is not the case, error field of
-struct NET is set to 1 and function exits. At the exit of sub-loop
-number of reruns already executed is reset to zero and another run
-of above vio_read function is attempted. If the function is run on
-Win32 and OS/2, and in the case that function flow was not interrupted
-and thread alarm is not in use, again the main loop is continued
-as long as there are bytes remaining. In the case that this function
-is executed on thread safe client program, then if another run
-should be made, which is decided by the output of vio_should_retry
-function, in which case the loop is continued. At the end of
-processing of the error from vio_read, error field of struct NET
-is set, and if on server last_errno field is set to ER_NET_READ_INTERRUPTED
-in the case that local bool variable (interrupted) is true or to
-ER_NET_ERROR_ON_READ. In case of such an error this function exits
-and returns error. In the case when there is no error, number of
-remaining bytes (remain) is decreased by the number of bytes read,
-which should be zero, but in case it is not the entire code is still
-in while (remain > 0) loop, which will be exited immediately if it
-is. This has been done to accommodate errors in the traffic level
-and for the very slow connections. Current position in field buff
-is also moved by the amount of bytes read by vio_read function, and
-global variable bytes_received is increased by the same value in a
-thread safe manner. When the loop that is run until necessary bytes
-are read (remain) is finished, then if external loop is in its first
-run, of the two, packet sequencing is tested for consistency by
-comparing the number contained at 4th byte in header with pkt_nr
-field. Header location is found at where_b offset to field_b. Usage
-of where_b is obligatory due to the possible compression usage. If
-there is no compression on a connection, then where_b is always 0.
-If there is a discrepancy, then first byte of the header is checked
-whether it is equal to 255, because when error is sent by the server,
-or by a client if it is sending data (like in LOAD DATA INFILE
-LOCAL...), then first byte in header is set to 255. If it is not
-255, then an error on packets being out of order is printed. In any
-case, on server, last_errno field is set to ER_NET_PACKETS_OUT_OF_ORDER
-and the function returns with an error, that is, the value returned is
-packet_error. If a check on serial number of packet is successful,
-pkt_nr field is incremented in order to enable checking packet order
-with next packet and if compression is used, uncompressed length
-is extracted from a proper position in header and returned in the
-second parameter of this function. Length of the packet is saved,
-for the purpose of a proper return value from this function. Still
-in the first iteration of the main loop, a check must be made if
-field buff could accommodate entire package that comes, in its
-compressed or uncompressed form. This is done in such a way, because
-zlib's compress and uncompress functions use the same memory area
-for compression and uncompression. Necessary field buff length is
-equal to current offset where data are (where_b which is zero for
-non-compression), plus the larger value of compressed or uncompressed
-package to be read in a second run. If this value is larger than
-the current length of field buff, which is read from field max_packet,
-then field buff has to be reallocated. If reallocation with net_realloc
-function fails, the function returns an error. Before a second
-loop is started, length to be read is set to the length of expected
-data and current position (pos) is set at where_b offset from field
-buff. At the end of function, if alarm is set, which is the case
-if it is run on server or on a client if a function is interrupted
-and another run of vio_read is attempted, alarm is ended and blocking
-state is restored from the saved local bool variable net_blocking.
-Function returns number of bytes read or the error (packet_error).
-
-
-Function name: my_net_read
-
-Parameters: struct NET *
-
-Return value: length of bytes read
-
-Function purpose: Highest level general purpose reading function
-
-Function description
-
-First, if compression is not used, my_real_read is called, with
-struct NET * a first parameter, and pointer to local ulong complen
-as a second parameter, but its value is not used here.  Number of
-bytes read is returned in local ulong variable len. read_pos field
-is set to an offset of value of where_b field from field buff.
-where_b field actually denotes where in field buff is the current
-packet. If returned number of bytes read (local variable len) does
-not signal that an error in packet transmission occurred (that is,
-it is not set to packet_error), then the string contained in read_pos
-is zero terminated. Simply, the end of the string starting at
-read_pos, and ending at read_pos + len, is set to zero. This is
-done in that way, because mysql_use_result expects a zero terminated
-string, and function returns with a value local variable len. This
-ends this function in the case that compression is not used and the
-remaining code is executed only if compression is enabled on the
-connection.
-
-In order to explain how a compressed packet logically is cut into
-meningful packets, the full meaning of several NET fields should
-be explained. First of all, fields in NET are used and not local
-variables, as all values should be saved between consecutive calls
-of this function. Simply, this function is called in order to return
-logical packets, but this function does not need to call my_real_read
-function everytime, because when a large packet is uncompressed,
-it may, but not necessarily so, contain several logical packets.
-Therefore, in order to preserve data on logical packets local
-variables are not used. Instead fields in NET struct are used. Field
-remain_in_buf denotes how many bytes of entire uncompressed packets
-is still contained within buff. field buf_length saves the value
-of the length of entire uncompressed packet. field save_char is
-used to save the character at the position where the packet ends,
-which character has to be replaced with a zero, '\0', in order to
-make a logical packet zero delimited, for mysql_use_result.  Field
-length stores the value of the length of compressed packet.  Field
-read_pos as usual, points to the current reading position.  This
-char * pointer is used by all functions that call this function in
-order to fetch their data. Field buff is not used for that purpose,
-but read_pos is used instead. This change was introduced with
-compression, when algorithm accommodated grouping of several packets
-together.
-
-Now that meanings of all relevant NET fields are explained,
-we can proceed with the flow of this function for the case when
-compression is active. First, if there are remaining portions of
-compressed packet in a field buff, saved character value is set at
-the position where zero char '\0' was inserted to enable the string
-to be zero delimited for mysql_use_result. Then a loop is started.
-In the first part of the loop, if there are remaining bytes, local
-uchar *pos variable is set at the current position in field buff
-where a new packet starts. This position is an (buf_length -
-remain_in_buf) offset in field buff. As it is possible that next
-logical packet is not read to the full length in the remaining of
-the field buf, several things had to be inspected. It should be
-noted that data that is read from net_real_read contains only logical
-packets containing 4 byte headers only, being 4 byte headers prepared
-by my_net_write or net_write_command. But, when written, logical
-packet could be so divided that only a part of header is read in.
-Therefore after pointer to the start of the next packet has been
-saved, a check is made whether number of remaining bytes in buffer
-is less than 4, being 3 bytes for length and one byte for packet
-number. If it is greater, then the length of the logical packet is
-extracted and saved a length field.  Then a check is made whether
-entire packet is contained within a buf, that is, a check is made
-that the logical packet is fully contained in the buffer. In that
-case, number of bytes remaining in buffer is decreased by the full
-length of logical packet (4 + length field), read_pos is moved
-forward by 4 bytes to skip header and be set at a beginning of data
-in logical packet, length field is saved for the value to be returned
-in function and the loop is exited. In the case that the entire
-logical packet is not contained within the buffer, then if length of
-the entire buffer differs from remaining length of logical packet,
-it (logical packet) is moved to the beginning of the field buff.
-If length of the entire buffer equals the remaining length of logical
-packet, where_b and buf_length fields are set to 0. This is done
-so that in both cases buffer is ready to accept next part of packet.
-
-In order to get a next part of a packet, still within a loop,
-my_real_read function is called and length of compressed packet is
-returned to a local len variable, and length of compressed data is
-returned in complen variable. In the case of non-compression value
-of complen is zero.  If packet_error is from my_real_read function,
-this function returns also with packet_error. If it is not a
-packet_error, my_uncompress function is called to uncompress data.
-It is called with offset of where_b data from field buff, as it is
-the position where compressed packet starts, and with len and complen
-values, being lengths of compressed and uncompressed data.  If there
-is no compression, 0 is returned for uncompressed size from
-my_real_read function, and my_uncompress wrapper function is made
-to skip zlib uncompress in that case. If error is returned from
-my_uncompress, error field is set to 1, if on server last_errno is
-set to ER_NET_UNCOMPRESS_ERROR and loop is exited and function
-returns with packet_error. If not, buf_length and remain_in_buf
-fields are set to the uncompressed size of buffer and the loop is
-continued. When the loop is exited save_char field is used to save
-the char at end of a logical packet, which is an offset of field
-len from position in field buff pointed by field read_pos, in order
-that zero char is set at the same position, for mysql_use_result.
-Function returns the length of the logical packet without its header.