SERVER-27209 Eliminate dangerous BSONElement string extraction methods

- Fix: Change return type of BSONObj::getStringField to include size
 (StringData vs. char*). A char* only contains the data with an ending NULL
 termination. Whereas a StringData contains data + size so caller knows how
 to interpret data if there are embedded NULLs.

- Cleanup: Remove old tag - CachedSizeTag - that disambiguated BSONElement ctors.
 A dangling reference to 'maxLen' in a comment led me to this historical issue.
 $ git log -S'maxLen' -- src/mongo/bson/bsonelement.h
 commit 0d38ef5
 Author: Mathias Stearn mathias@10gen.com
 Date: Tue Dec 19 14:23:08 2017 -0500

 SERVER-32302 Compute BSONElement sizes eagerly

- Test: Add tests for NULL bytes being returned by getStringField

  - $ ninja -j400 +bson_obj_test

- Cleanup: Move BSONElement::valuestr() from public to private

- Cleanup: Remove BSONElement::valuestrsafe()

- Cleanup: Remove all external callers of valuestr/valuestrsafe and cleanup
 their callsites with better alternatives.

- Cleanup: Make multi-line BSONElement & BSONObj public API comments
 conform to style guidelines

- Nit: Fix spelling in a comment

1 files changed, 1 insertions, 1 deletions

diff --git a/src/mongo/db/write_concern_options.cpp b/src/mongo/db/write_concern_options.cpp
index baf56a1a669..53883d0cba0 100644
--- a/src/mongo/db/write_concern_options.cpp
+++ b/src/mongo/db/write_concern_options.cpp
@@ -179,7 +179,7 @@ StatusWith<WriteConcernOptions> WriteConcernOptions::parse(const BSONObj& obj) {
         writeConcern.notExplicitWValue = false;
     } else if (wEl.type() == String) {
         writeConcern.wNumNodes = 0;
-        writeConcern.wMode = wEl.valuestrsafe();
+        writeConcern.wMode = wEl.str();
         writeConcern.notExplicitWValue = false;
     } else if (wEl.eoo() || wEl.type() == jstNULL || wEl.type() == Undefined) {
         writeConcern.wNumNodes = 1;