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

manifest

@@ -1,5 +1,5 @@
-C Fix\sthe\sversion\snumber\sin\sthe\sTEA\sconfigure\sscript.\s\sThis\sshould\shave\nbeen\schanged\sby\s[1481baf3d55effcc]\sthree\scheck-ins\sago.\nIt\sis\sunclear\show\stesting\smissed\sthis.
+C When\sbacking\sout\sa\scharacter\sin\sa\sconstructed\sstring\sin\sJSON,\sfirst\smake\ssure\nthe\sstring\shas\snot\sbeen\sreset\sby\son\sOOM.\ndbsqlfuzz\s2fffbea91a5376526ea118d4fe4188c8dd35e317.
-D 2024-01-20T12:00:20.372
+D 2024-01-20T12:13:00.530
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -698,7 +698,7 @@ F src/hash.h 3340ab6e1d13e725571d7cee6d3e3135f0779a7d8e76a9ce0a85971fa3953c51
 F src/hwtime.h f9c2dfb84dce7acf95ce6d289e46f5f9d3d1afd328e53da8f8e9008e3b3caae6
 F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
 F src/insert.c 3f0a94082d978bbdd33c38fefea15346c6c6bffb70bc645a71dc0f1f87dd3276
-F src/json.c 624824b0c405dc64bb371107f21baf1d00a6b609cbdb16feaa2338a335bf981b
+F src/json.c 5405e50cf0d7aeae12ac5b46e0fc9b3757b3b9cb4885f1a73ec7afeac99b9759
 F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
 F src/loadext.c 7432c944ff197046d67a1207790a1b13eec4548c85a9457eb0896bb3641dfb36
 F src/main.c 438b95162acfa17b7d218f586f5bde11d6ae82bcf030c9611fc537556870ad6b
@@ -2159,8 +2159,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P b06ab46a9ee98719159ed3e05cdfbf26281353d781206f56ed7cb12859210fed
+P eaf2cf73fca3355edd05fef5b0d0262a6555633908794068805d12b1948beedc
-R 9501c38a1e8bd841e94256d593af54ad
+R 8f8b8c466d5567f67ab6487c681d59e2
 U drh
-Z 968fbfadacc13465ad30d7b8182c0acc
+Z fda57e08b93251c93aba9abc8bd9967a
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-eaf2cf73fca3355edd05fef5b0d0262a6555633908794068805d12b1948beedc
+666690eb433fe38fa527ccbbb8e2c00041a33939da4f6b8bfb737d664f28f0d8

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);