opencensus-specs

Tag Context API

TODO(sebright): Add more detail to the Tag Context summary, including how it relates to the current context.

TagContext is an abstract data type that represents a collection of tags. A TagContext can be used to label anything that is associated with a specific operation, such as an HTTP request. Each tag is composed of a key (TagKey), and a value (TagValue). A TagContext represents a map from keys to values, i.e., each key is associated with exactly one value, but multiple keys can be associated with the same value. TagContext is serializable, and it represents all of the information that must be propagated across process boundaries.

TagKey

A string or string wrapper, with some restrictions:

• Must contain only printable ASCII (codes between 32 and 126, inclusive).
• Must have length greater than zero and less than 256.

TagValue

A string or string wrapper with the same restrictions as TagKey, except that it is allowed to be empty.

Serialization

This section applies to all serialization formats. See https://github.com/census-instrumentation/opencensus-specs/tree/master/encodings for specific formats.

• The serialization format must preserve the TagKey-TagValue mapping.
• A TagContext can only be serialized or deserialized if the combined size of its keys and values is at most 8192 characters (8192 bytes). The size restriction applies to the deserialized tags so that the set of serializable TagContexts is independent of the serialization format.

Error handling

• There are no partial failures. The result of serialization or deserialization should always be a complete TagContext or an error. The type of error reporting depends on the language.
• Serialization should result in an error if the TagContext does not meet the size restriction above.
• Deserialization should result in an error if the serialized TagContext
  • cannot be parsed.
  • contains a TagKey or TagValue that does not meet the restrictions above.
  • does not meet the size restriction above.

This site is open source. Improve this page.