When backing out a character in a constructed string in JSON, first make sure

the string has not been reset by on OOM.
dbsqlfuzz 2fffbea91a5376526ea118d4fe4188c8dd35e317.

FossilOrigin-Name: 666690eb433fe38fa527ccbbb8e2c00041a33939da4f6b8bfb737d664f28f0d8

1 files changed, 17 insertions, 7 deletions

diff --git a/src/json.c b/src/json.c
index 97cf5fe28..d33692466 100644
--- a/src/json.c
+++ b/src/json.c
@@ -589,6 +589,16 @@ static void jsonAppendChar(JsonString *p, char c){
   }
 }
 
+/* Remove a single character from the end of the string
+*/
+static void jsonStringTrimOneChar(JsonString *p){
+  if( p->eErr==0 ){
+    assert( p->nUsed>0 );
+    p->nUsed--;
+  }
+}
+
+
 /* Make sure there is a zero terminator on p->zBuf[]
 **
 ** Return true on success.  Return false if an OOM prevents this
@@ -596,7 +606,7 @@ static void jsonAppendChar(JsonString *p, char c){
 */
 static int jsonStringTerminate(JsonString *p){
   jsonAppendChar(p, 0);
-  p->nUsed--;
+  jsonStringTrimOneChar(p);
   return p->eErr==0;
 }
 
@@ -2261,7 +2271,7 @@ static u32 jsonTranslateBlobToText(
         j = jsonTranslateBlobToText(pParse, j, pOut);
         jsonAppendChar(pOut, ',');
       }
-      if( sz>0 ) pOut->nUsed--;
+      if( sz>0 ) jsonStringTrimOneChar(pOut);
       jsonAppendChar(pOut, ']');
       break;
     }
@@ -2275,7 +2285,7 @@ static u32 jsonTranslateBlobToText(
         jsonAppendChar(pOut, (x++ & 1) ? ',' : ':');
       }
       if( x & 1 ) pOut->eErr |= JSTRING_MALFORMED;
-      if( sz>0 ) pOut->nUsed--;
+      if( sz>0 ) jsonStringTrimOneChar(pOut);
       jsonAppendChar(pOut, '}');
       break;
     }
@@ -4403,7 +4413,7 @@ static void jsonArrayCompute(sqlite3_context *ctx, int isFinal){
       if( isFinal ){
         if( !pStr->bStatic ) sqlite3RCStrUnref(pStr->zBuf);
       }else{
-        pStr->nUsed--;
+        jsonStringTrimOneChar(pStr);
       }
       return;
     }else if( isFinal ){
@@ -4413,7 +4423,7 @@ static void jsonArrayCompute(sqlite3_context *ctx, int isFinal){
       pStr->bStatic = 1;
     }else{
       sqlite3_result_text(ctx, pStr->zBuf, (int)pStr->nUsed, SQLITE_TRANSIENT);
-      pStr->nUsed--;
+      jsonStringTrimOneChar(pStr);
     }
   }else{
     sqlite3_result_text(ctx, "[]", 2, SQLITE_STATIC);
@@ -4523,7 +4533,7 @@ static void jsonObjectCompute(sqlite3_context *ctx, int isFinal){
       if( isFinal ){
         if( !pStr->bStatic ) sqlite3RCStrUnref(pStr->zBuf);
       }else{
-        pStr->nUsed--;
+        jsonStringTrimOneChar(pStr);
       }
       return;
     }else if( isFinal ){
@@ -4533,7 +4543,7 @@ static void jsonObjectCompute(sqlite3_context *ctx, int isFinal){
       pStr->bStatic = 1;
     }else{
       sqlite3_result_text(ctx, pStr->zBuf, (int)pStr->nUsed, SQLITE_TRANSIENT);
-      pStr->nUsed--;
+      jsonStringTrimOneChar(pStr);
     }
   }else{
     sqlite3_result_text(ctx, "{}", 2, SQLITE_STATIC);