Escape control characters in JSON.

Fix for ticket [ad2559db380abf8].

FossilOrigin-Name: 4f1b5229a3bbc9d40b7433a5eb3139d59d31dcb1

ext/misc/json1.c

@@ -276,10 +276,33 @@ static void jsonAppendString(JsonString *p, const char *zIn, u32 N){
   if( (N+p->nUsed+2 >= p->nAlloc) && jsonGrow(p,N+2)!=0 ) return;
   p->zBuf[p->nUsed++] = '"';
   for(i=0; i<N; i++){
-    char c = zIn[i];
+    unsigned char c = ((unsigned const char*)zIn)[i];
     if( c=='"' || c=='\\' ){
+      json_simple_escape:
       if( (p->nUsed+N+3-i > p->nAlloc) && jsonGrow(p,N+3-i)!=0 ) return;
       p->zBuf[p->nUsed++] = '\\';
+    }else if( c<=0x1f ){
+      static const char aSpecial[] = {
+         0, 0, 0, 0, 0, 0, 0, 0, 'b', 't', 'n', 0, 'f', 'r', 0, 0,
+         0, 0, 0, 0, 0, 0, 0, 0,   0,   0,   0, 0,   0,   0, 0, 0
+      };
+      assert( sizeof(aSpecial)==32 );
+      assert( aSpecial['\b']=='b' );
+      assert( aSpecial['\f']=='f' );
+      assert( aSpecial['\n']=='n' );
+      assert( aSpecial['\r']=='r' );
+      assert( aSpecial['\t']=='t' );
+      if( aSpecial[c] ){
+        c = aSpecial[c];
+        goto json_simple_escape;
+      }
+      if( (p->nUsed+N+7+i > p->nAlloc) && jsonGrow(p,N+7-i)!=0 ) return;
+      p->zBuf[p->nUsed++] = '\\';
+      p->zBuf[p->nUsed++] = 'u';
+      p->zBuf[p->nUsed++] = '0';
+      p->zBuf[p->nUsed++] = '0';
+      p->zBuf[p->nUsed++] = '0' + (c>>4);
+      c = "0123456789abcdef"[c&0xf];
     }
     p->zBuf[p->nUsed++] = c;
   }