Break is goto in disguise

On the python list there was a discussion about break.  I made the comment that break is just a euphemism for goto.  I thought that this would be a commonplace. However google does not give many useful hits for this.

So thought I'd cook up an example.
Here is Apple's famous SSL-bug in shortform

It is discussed in many places 

static OSStatus
SSLVerifySignedServerKeyExchange(SSLContext *ctx, bool isRsa,  

                                  SSLBuffer signedParams,
                                 uint8_t *signature, UInt16 signatureLen)
{
    OSStatus        err;

    signedHashes.data = 0;
    hashCtx.data = 0;


    hashOut.data = hashes + SSL_MD5_DIGEST_LEN;
    hashOut.length = SSL_SHA1_DIGEST_LEN;
    if ((err = SSLFreeBuffer(&hashCtx)) != 0)
        goto fail;


    if ((err = ReadyHash(&SSLHashSHA1, &hashCtx)) != 0)
        goto fail;
    if ((err = SSLHashSHA1.update(&hashCtx, &clientRandom)) != 0)
        goto fail;
    if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0)
        goto fail;
    if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
        goto fail;
        goto fail;          //<----- OOOOOOPSSSSS!!
    if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0)
        goto fail;

    err = sslRawVerify(ctx,               // <--- Important Code
                       ctx->peerPubKey,   // That needs to run
                       dataToSign,        // Missed
                       dataToSignLen,
                       signature,
                       signatureLen);
    if(err) {
        sslErrorLog("SSLDecodeSignedServerKeyExchange: sslRawVerify "
                    "returned %d\n", (int)err);
        goto fail;
    }

fail:
    SSLFreeBuffer(&signedHashes);
    SSLFreeBuffer(&hashCtx);
    return err;

}

Now we just slightly hypotheticalize it by enclosing in a loop:

static OSStatus
SSLVerifySignedServerKeyExchange(SSLContext *ctx, bool isRsa,

                                 SSLBuffer signedParams,
                                 uint8_t *signature, UInt16 signatureLen)
{
    OSStatus        err;

    signedHashes.data = 0;
    hashCtx.data = 0;


    hashOut.data = hashes + SSL_MD5_DIGEST_LEN;
    hashOut.length = SSL_SHA1_DIGEST_LEN;
    :
    :
    while (somethin)  { 

       if ((err = SSLFreeBuffer(&hashCtx)) != 0)
            goto fail;

       if ((err = ReadyHash(&SSLHashSHA1, &hashCtx)) != 0)
            goto fail;
        if ((err = SSLHashSHA1.update(&hashCtx, &clientRandom)) != 0)
            goto fail;
        if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0)
            goto fail;
        if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
            goto fail; 
            goto fail;
        if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0)
            goto fail;

        err = sslRawVerify(ctx,
                           ctx->peerPubKey,
                           dataToSign,   
                           dataToSignLen,
                           signature,
                           signatureLen);

        if(err) {
            sslErrorLog("SSLDecodeSignedServerKeyExchange: sslRawVerify "
                        "returned %d\n", (int)err);
            goto fail;
        }
    }
fail:
    SSLFreeBuffer(&signedHashes);
    SSLFreeBuffer(&hashCtx);
    return err;
}

And voila! We can change the gotos to breaks with the buggy behavior!

static OSStatus
SSLVerifySignedServerKeyExchange(SSLContext *ctx, bool isRsa,

                                 SSLBuffer signedParams,
                                 uint8_t *signature, UInt16 signatureLen)
{
    OSStatus        err;

    signedHashes.data = 0;
    hashCtx.data = 0;


    hashOut.data = hashes + SSL_MD5_DIGEST_LEN;
    hashOut.length = SSL_SHA1_DIGEST_LEN;

    :
    :
    while (somethin)  {

        if ((err = SSLFreeBuffer(&hashCtx)) != 0)
            break;

        if ((err = ReadyHash(&SSLHashSHA1, &hashCtx)) != 0)
            break;
        if ((err = SSLHashSHA1.update(&hashCtx, &clientRandom)) != 0)
            break;
        if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0)
            break;
        if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
            break;
            break;               //<--- Same Oops as goto!!
        if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0)
            break;

        err = sslRawVerify(ctx,
                           ctx->peerPubKey,      // Missed
                           dataToSign,           // just the same
                           dataToSignLen,        // whether you spell it goto
                           signature,            // or break :-)
                           signatureLen);
        if(err) {
            sslErrorLog("SSLDecodeSignedServerKeyExchange: sslRawVerify "
                        "returned %d\n", (int)err);
            break;
        }
    }
    // What was fail: label; now implicit
    SSLFreeBuffer(&signedHashes);
    SSLFreeBuffer(&hashCtx);
    return err;
} 

From this example many people have concluded many things... I may write about that subsequently

For now lets just agree that break is not very different from goto

[Also thought I'd massage the same example to show that continue is no different.  But that evidently requires more work...]