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A CouchDB Query Server Runtime build with ChakraCore
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README.md

Couch Chakra

couch-chakra is a (sort of) drop in replacement for the CouchDB Query Server Runtime couchjs build on top of Microsoft's ChakraCore.

Motivation

  • Learning the inner workings of the CouchDB Query Server Subsystem
  • Get my C skills back out of the closet
  • Have fun working with fancy technology
  • ChakraCore is used in Microsoft's DocumentDB

Status

  • It currently passes all tests in query_server_spec.rb
  • Has proper sandboxing
  • Deals with the anonymous function issue, aka COUCHDB-1397
  • NO for each, so you'll have to patch views.js before running the query server tests
  • NO cURL bindings
  • NO -T command line flag for test suite specific functions
  • NO -u command line argument
  • NO --no-eval command line argument

Discussion

It's not the first alternative suggested to the existing Query Server Runtime. There's at least one based on NodeJS which started an interesting discussion at COUCHDB-1894. A couple of important aspects for a Query Server Runtime can be extracted from it:

  • Sandboxing
  • The anonymous function issue
  • Versioning of the runtime
  • Ease of installation

The anonymous function issue, aka COUCHDB-1397

In short, CouchDB makes use of a now disabled feature of the SpiderMonkey runtime which allowed anonymous functions to appear in global scope. This made for a really nice way of declaring view functions in CouchDB, however it was always invalid behavior and no modern runtime is going to add this feature again.

Couch-Chakra has two propositions to work around this issue.

The legacy mode

Code written in the old CouchDB style function(doc, view) {...} is considered legacy. Running Couch-Chakra with the -L flag parses the provided script with a patched version of esprima, rewrites the resulting AST and generates a compliant version of the function with the help of escodegen. This is quite a huge machinery and I do hope that a modern JS runtime can make up for the performance hit, however I can't provide any figures.

ES6 arrow functions

Fortunately ES6 introduced so called arrow functions which seem to be a perfect fit for CouchDB map functions. Replacing function(doc, view) {...} by (doc, view) => {} is a rather simple modification, simple to explain and transforms the not-so-valid JavaScript into perfectly ES6 code which can be run without the legacy mode enabled.

Build it

Couch-Chakra builds with current master of ChakraCore (I used cb7817b) which I'm afraid you have to build from sources. Once built, modify the first two lines of the Makefile of this project and run make. If you want to run the (two very simplistic) tests, run make check . Everythings is very early, it builds on my machine™ which runs on MacOS X 10.11.6 with latest xcode.

References

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