Moving XML parser from aws-c-auth into aws-c-common #674
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justinboswell
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Jul 30, 2020
…s changes to tests to be more consistent.
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I know it's a lot more work, but should these go into a new repo, instead of aws-c-common? |
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justinboswell
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Jul 31, 2020
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**Issue:** It's hard to report errors with the current API. Errors are being accidentally ignored, and some errors are never checked (perhaps because it was too much effort?). **Diagnosis:** The current callback returns `bool` of whether to continue parsing, rather than our typical `int/AWS_OP_SUCCESS/aws_raise_error()` [error handling](https://github.com/awslabs/aws-c-common/blob/b1ef77c1790a8776b58ae5ae57f90e9534b78991/README.md#error-handling). This seems like a simple design. But the inconsistency in return type leads to errors being [mistakenly swallowed](awslabs/aws-c-s3#330 (comment)). And it makes it hard when you do want to "bubble up" an error from the callback. Callbacks needs to store a custom `error_code` in their `user_data` to report an error. Most callbacks never bothered to do this, maybe because it was extra work? **Description of changes:** - XML traversal callback returns `int` instead of `bool`. - If a callback fails, the whole parse() fails. - You can no longer stop parsing without causing failure. But in nearly all use-cases we were stopping due to error. I found 1 case where we stopped because we found what we were looking for. But in this case, it didn't really hurt to continue parsing. The reduced complexity seemed worth the change. - Remove ~aws_xml_parser_new(), aws_xml_parser_destroy(), aws_xml_parser_parse()~, replace with `aws_xml_parse()`. - The new() and destroy() calls were unnecessary. Removing them simplifies use. - `aws_xml_node_get_name()` just returns `aws_byte_cursor()`, instead of ~int~ - This can't fail. Changing the signature simplifies use. - Raise `AWS_ERROR_INVALID_XML` instead of ~AWS_ERROR_MALFORMED_INPUT_STRING~ - This change is more wishy-washy. It seemed useful to get this new, more specific, error code if it bubbling up from deep within some larger operation, like an S3 meta-request. **API BREAK:** We don't know any external uses of this API, so it seems safe to change. The API is only intended for internal use by the aws-c libraries, which are being fixed up now. This API was quickly written as private code in aws-c-auth (awslabs/aws-c-auth#40), then moved to public in aws-c-common (#674) when aws-c-s3 also needed to parse XML. The fact that it was originally private is why this API didn't get more scrutiny originally.
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Description of changes:
Adding XML parser from aws-c-auth. Made minor changes for naming, also made a couple of types opaque and added accessors.
Justification for leaving aws_xml_attribute visible: it seems reasonable that we could expose an attribute as a name/value pair, and that this would be less awkward than needing a get-attribute, get-name, get-value each time when needing to use a single attribute. (But I'm open to making this opaque too!)
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.