Revert "change the encoder interface -- encoders always append the null byte,"

This reverts commit 1aa6c288.

The wb interface adds a null byte, so we were getting two of them. Going
back to the requirement that the caller of an encoder adds a null
byte, which means that the blob.encode() method must do so as well.

src/base64.c

@@ -182,7 +182,6 @@ base64_encode(const enum encoding enc, char *restrict const buf,
 	}
 
 	assert(outlen > 0);
-	*p++ = '\0';
 	return p - buf;
 }
 

src/hex.c

@@ -134,7 +134,6 @@ hex_encode(const enum encoding enc, char *restrict const buf,
 		*p++ = alphabet[in[i] & 0x0f];
 	}
 
-	*p++ = '\0';
 	return p - buf;
 }
 

src/id.c

@@ -48,7 +48,6 @@ id_encode(const enum encoding enc, char *restrict const buf,
 		return 0;
 
 	memcpy(buf, in, inlen);
-	buf[inlen] = '\0';
 	return inlen;
 }
 

src/vmod_blobcode.c

@@ -270,6 +270,7 @@ vmod_blob_encode(VRT_CTX, struct vmod_blobcode_blob *b, VCL_ENUM encs)
 		AZ(pthread_mutex_lock(&b->lock));
 		if (b->encoding[enc] == NULL) {
 			ssize_t len;
+
 			switch(enc) {
 			case IDENTITY:
 				len = b->blob.len + 1;
@@ -296,15 +297,16 @@ vmod_blob_encode(VRT_CTX, struct vmod_blobcode_blob *b, VCL_ENUM encs)
 				if (b->encoding[enc] == NULL)
 					ERRNOMEM(ctx, "cannot encode");
 				else {
-					len = encode(enc,
-						     (void *) b->encoding[enc],
-						     len, b->blob.priv,
-						     b->blob.len);
+					const char *s = b->encoding[enc];
+					len = encode(enc, (void *) s, len,
+						     b->blob.priv, b->blob.len);
 					assert(len >= 0);
 					if (len == 0) {
-						free((void *) b->encoding[enc]);
+						free((void *) s);
 						b->encoding[enc] = "";
 					}
+					else
+						*((char *)s + len) = '\0';
 				}
 			}
 		}

src/vmod_blobcode.h

@@ -60,9 +60,8 @@
  *
  * The regions pointed to by buf and in MUST NOT overlap (this is the
  * contract imposed by restrict).
- * An encoder SHALL append the terminating null byte if the length of
- * the encoding is greater than 0; if the length is 0, the encoder
- * SHALL NOT write the null byte.
+ * An encoder SHALL NOT append the terminating null byte (this must
+ * be done by the caller).
  *
  * Returns:
  * -1, if there is insufficient space at buf, *including* space for the