der: add Reader::read_value, auto-nest DecodeValue
#1877
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cc @dishmaker |
Previously `der` lacked an abstraction for automatically setting up nested readers when decoding values, so every `DecodeValue` impl ended up handling its own nesting. This adds a new provided method to the `Reader` trait which automatically handles nesting. This change is backwards compatible in that if a `DecodeValue` impl does its own `reader.read_nested`, it will just create another nested reader of the same length, which is redundant but doesn't break anything. However, we should remove all of the `read_nested` calls from `DecodeValue` impls with this approach anyway as they're redundant. Using a provided method for this opens up the possibility of reader-specific handling of field decoding, which would be useful for addressing indefinite length handling for BER decoding (#779).
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Note: this pretty much eliminates any direct calls to |
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Looks good. Removes boilerplate 👍 Maybe I will add negative tests for bad nesting (i.e. when read_nested should fail). |
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@dishmaker more testing around failure cases in nested message handling would be greatly appreciated |
tarcieri
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This was added in #1877 but the real value of that PR was the automatic `read_nested` on `DecodeValue` impls. `Reader::read_value` isn't actually necessary for that at all. It may be useful in the future if we introduce a BER reader that can handle decoding constructed e.g. strings from indefinite length encoding, but since we don't actually have anything like that yet, removing this avoids some unnecessary duplication and API surface for the `Reader`.
tarcieri
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Jun 21, 2025
This was added in #1877 but the real value of that PR was the automatic `read_nested` on `DecodeValue` impls. `Reader::read_value` isn't actually necessary for that at all. It may be useful in the future if we introduce a BER reader that can handle decoding constructed e.g. strings from indefinite length encoding, but since we don't actually have anything like that yet, removing this avoids some unnecessary duplication and API surface for the `Reader`.
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Previously
derlacked an abstraction for automatically setting up nested readers when decoding values, so everyDecodeValueimpl ended up handling its own nesting.This adds a new provided method to the
Readertrait which automatically handles nesting.This change is backwards compatible in that if a
DecodeValueimpl does its ownreader.read_nested, it will just create another nested reader of the same length, which is redundant but doesn't break anything. However, we should remove all of theread_nestedcalls fromDecodeValueimpls with this approach anyway as they're redundant.Using a provided method for this opens up the possibility of reader-specific handling of field decoding, which would be useful for addressing indefinite length handling for BER decoding (#779).