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add option to not parse beyond end of structure #435

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merged 4 commits into from
Jun 9, 2022
Merged

add option to not parse beyond end of structure #435

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add option to not parse beyond end of structure
petar May 26, 2022
d7f1bd2
add test
petar Jun 7, 2022
9ec0389
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petar Jun 7, 2022
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add to test
petar Jun 7, 2022
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7 changes: 7 additions & 0 deletions codec/dagjson/unmarshal.go
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,10 @@ type DecodeOptions struct {
// If true, parse DAG-JSON `{"/":{"bytes":"base64 bytes..."}}` as a Bytes kind
// node rather than nested plain maps
ParseBytes bool

// If true, the decoder stops reading from the stream at the end of the JSON structure.
// I.e. it does not slurp remaining whitespaces and EOF.
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DontParseBeyondEnd bool
}

// Decode deserializes data from the given io.Reader and feeds it into the given datamodel.NodeAssembler.
Expand All @@ -43,6 +47,9 @@ func (cfg DecodeOptions) Decode(na datamodel.NodeAssembler, r io.Reader) error {
if err != nil {
return err
}
if cfg.DontParseBeyondEnd {
return nil
}
Comment on lines +53 to +55
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@petar IIUC this is perhaps a nice config option, but only slightly helps fix the problem you're likely currently worrying about (i.e. streaming decodes of multiple dag-json objects for Reframe using Edelweiss).

Since the specific application format (in this case Reframe's HTTP+dag-json transport) has its own way of dealing with concatenating dag-json blobs (in this case appending \n) you're going to need some custom code anyhow to parse the \n.

At that point is it so different from just using Unmarshal(na, json.NewDecoder(r), cfg) directly and then trying to slurp up one more \n before continuing instead of using Decode?

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The issue with this proposal is that json.NewDecoder won't decode bytes and other IPLD-specific objects. Right?

The solution to Edelweiss' problem could be composed of two steps:

  • this PR, which makes sure nothing is slurped after the JSON object, and
  • a manual reader.ReadChar, following every invocation of ipld.StreamingUnmarshal(dagjson.Decoder, ...) in the Edelweiss-generated code for reading multiple \n-separated results.

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I just wanted to flag more concretely that this PR just allows for using:

DecodeOptions{ ParseLinks : true, ParseBytes: true, DontParseBeyondEnd : true }.Decode(na, r)

rather than:

Unmarshal(na, json.NewDecoder(r), DecodeOptions{ ParseLinks : true, ParseBytes: true }).

Is this config mostly about helping discoverability so people know how to do this (i.e. is the Unmarshal code path not obvious enough)?

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It turns out that Unmarshal is deprecated.

// Slurp any remaining whitespace.
// This behavior may be due for review.
// (This is relevant if our reader is tee'ing bytes to a hasher, and
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