Symfony\Component\Yaml\Inline::evaluateScalar() breaks ISO 8601 dates #6275

bartfeenstra opened this Issue Dec 12, 2012 · 5 comments


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Symfony\Component\Yaml\Inline::evaluateScalar() uses Symfony\Component\Yaml\Inline::getTimestampRegex() to determine whether a scalar value contains a date in what seems to be the ISO 8601 format (getTimestampRegex() is badly documented) and if it does, it converts it to a Unix timestamp.
The problem is that this conversion is conceptually impossible for a number of reasons:

  • ISO 8601 dates and Unix timestamps use different formats. Converting one to the other may break systems that expect a particular format.
  • Unix timestamps do not support dates before 1970, while ISO 8601 does. This means data loss.

Suggested solution: remove the feature entirely.

stof commented Dec 12, 2012

The feature should not be removed as handling ISO 8601 values a dates is part of the YAML spec. If you want to keep the string, you have to quote it.

I might not be a YAML expert, but how is converting a value that can or cannot (e.g. dates before 1970) be converted to a Unix timestamp to a Unix timestamp part of the specifications? I did a quick search of the 1.0, 1.1 and 1.2 documentation and couldn't find anything about special handling for ISO 8601 or Unix timestamps.

asm89 commented Dec 12, 2012

@bartfeenstra Dates before 1970 are represented by negative numbers. See the PR I created with a test showing that dates before 1970 work.

Are you having issues with this?

@fabpot fabpot added a commit that referenced this issue Dec 12, 2012
@fabpot fabpot merged branch asm89/yaml-inline (PR #6277)
This PR was merged into the master branch.


2f07966 [Yaml] Add test showing that dates before 01 Jan 1970 are correctly parsed


[Yaml] Add test showing that dates before 01 Jan 1970 are correctly parsed

Bug fix: no
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes

Adds a test related to issue #6275, showing that the Yaml inline parsing supports ISO 8601 dates before 1980.

It appears that YYYY-MM-DD formats need to be quoted so Yaml doesn't convert them. YYYY-MM formats can be unquoted. My problems occured after manually altering some configuration files and not quoting YYYY-MM-DDD formats. A classic example of pebkac.

Thank you, stof and asm89, for your time spent on this issue!

Now that my issues are solved, I still have a few questions though:

  • Unix timestamps in PHP, which are essentially 32bits signed integers, have a very limited minimum value. -2147483647 (minimum value) / 86400 (number of seconds in a day) / 365 (days in a year) = roughly 68 years before 1970, so when converting any ISO8601 date before roughly 1902 on a 32bit system, this should result in an overflow. On 64bit systems the range of a Unix timestamp exceeds that of the default ISO 8601 format and this problem does not occur.
  • Why does Yaml convert some date formats (Symfony\Component\Yaml\Inline::getTimestampRegex() says "Unix timestamp", which is incorrect, not does it really describe what the pattern should match), but not all? To be more specific: why does it convert YYYY-MM-DD, but not YYYY-MM?
stof commented Dec 12, 2012

@bartfeenstra because of the format specified in the YAML spec for timestamps:

@fabpot fabpot closed this in 04d95a5 Dec 15, 2012
@fabpot fabpot added a commit that referenced this issue Feb 18, 2016
@fabpot fabpot feature #17836 [Yaml] support to parse and dump DateTime objects (xab…

This PR was merged into the 3.1-dev branch.


[Yaml] support to parse and dump DateTime objects

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6275, #8580, #11838, #14420
| License       | MIT
| Doc PR        | TODO


7e1c6c4 [Yaml] support to parse and dump DateTime objects
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