mirror of https://github.com/grpc/grpc.git
Craig Tiller
9 years ago
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# gRPC (Core) Compression Cookbook |
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|
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## Introduction |
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|
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This document describes compression as implemented by the gRPC C core. See [the |
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full compression specification](compression.md) for details. |
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|
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### Intended Audience |
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|
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Wrapped languages developers, for the purposes of supporting compression by |
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interacting with the C core. |
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|
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## Criteria for GA readiness |
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|
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1. Be able to set compression at [channel](#per-channel-settings), |
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[call](#per-call-settings) and [message](#per-message-settings) level. |
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In principle this API should be based on _compression levels_ as opposed to |
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algorithms. See the discussion [below](#level-vs-algorithms). |
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1. Have unit tests covering [the cases from the |
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spec](https://github.com/grpc/grpc/blob/master/doc/compression.md#test-cases). |
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1. Interop tests implemented and passing on Jenkins. The two relevant interop |
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test cases are |
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[large_compressed_unary](https://github.com/grpc/grpc/blob/master/doc/interop-test-descriptions.md#large_compressed_unary) |
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and |
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[server_compressed_streaming](https://github.com/grpc/grpc/blob/master/doc/interop-test-descriptions.md#server_compressed_streaming). |
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|
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## Summary Flowcharts |
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|
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The following flowcharts depict the evolution of a message, both _incoming_ and |
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_outgoing_, irrespective of the client/server character of the call. Aspects |
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still not symmetric between clients and servers (e.g. the [use of compression |
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levels](https://github.com/grpc/grpc/blob/master/doc/compression.md#compression-levels-and-algorithms)) |
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are explicitly marked. The in-detail textual description for the different |
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scenarios is described in subsequent sections. |
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|
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## Incoming Messages |
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|
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 |
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|
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## Outgoing Messages |
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|
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 |
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|
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## Levels vs Algorithms |
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|
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As mentioned in [the relevant discussion on the spec |
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document](https://github.com/grpc/grpc/blob/master/doc/compression.md#compression-levels-and-algorithms), |
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compression _levels_ are the primary mechanism for compression selection _at the |
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server side_. In the future, it'll also be at the client side. The use of levels |
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abstracts away the intricacies of selecting a concrete algorithm supported by a |
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peer, on top of removing the burden of choice from the developer. |
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As of this writing (Q2 2016), clients can only specify compression _algorithms_. |
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Clients will support levels as soon as an automatic retry/negotiation mechanism |
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is in place. |
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|
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## Per Channel Settings |
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|
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Compression may be configured at channel creation. This is a convenience to |
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avoid having to repeatedly configure compression for every call. Note that any |
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compression setting on individual [calls](#per-call-settings) or |
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[messages](#per-message-settings) overrides channel settings. |
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|
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The following aspects can be configured at channel-creation time via channel arguments: |
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|
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#### Disable Compression _Algorithms_ |
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|
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Use the channel argument key |
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`GRPC_COMPRESSION_CHANNEL_ENABLED_ALGORITHMS_BITSET` (from |
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[`grpc/impl/codegen/compression_types.h`](https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h)), |
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takes a 32 bit bitset value. A set bit means the algorithm with that enum value |
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according to `grpc_compression_algorithm` is _enabled_. |
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For example, `GRPC_COMPRESS_GZIP` currently has a numeric value of 2. To |
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enable/disable GZIP for a channel, one would set/clear the 3rd LSB (eg, 0b100 = |
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0x4). Note that setting/clearing 0th position, that corresponding to |
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`GRPC_COMPRESS_NONE`, has no effect, as no-compression (a.k.a. _identity_) is |
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always supported. |
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Incoming messages compressed (ie, encoded) with a disabled algorithm will result |
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in the call being closed with `GRPC_STATUS_UNIMPLEMENTED`. |
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|
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#### Default Compression _Level_ |
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|
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**(currently, Q2 2016, only applicable for server side channels. It's ignored |
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for clients.)** |
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Use the channel argument key `GRPC_COMPRESSION_CHANNEL_DEFAULT_LEVEL` (from |
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[`grpc/impl/codegen/compression_types.h`](https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h)), |
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valued by an integer corresponding to a value from the `grpc_compression_level` |
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enum. |
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|
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#### Default Compression _Algorithm_ |
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|
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Use the channel argument key `GRPC_COMPRESSION_CHANNEL_DEFAULT_ALGORITHM` (from |
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[`grpc/impl/codegen/compression_types.h`](https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h)), |
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valued by an integer corresponding to a value from the `grpc_compression_level` |
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enum. |
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|
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## Per Call Settings |
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|
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### Compression **Level** in Call Responses |
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|
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The server requests a compression level via initial metadata. The |
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`send_initial_metadata` `grpc_op` contains a `maybe_compression_level` field |
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with two fields, `is_set` and `compression_level`. The former must be set when |
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actively choosing a level to disambiguate the default value of zero (no |
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compression) from the proactive selection of no compression. |
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|
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The core will receive the request for the compression level and automatically |
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choose a compression algorithm based on its knowledge about the peer |
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(communicated by the client via the `grpc-accept-encoding` header. Note that the |
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absence of this header means no compression is supported by the client/peer). |
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|
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### Compression **Algorithm** in Call Responses |
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|
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**Server should avoid setting the compression algorithm directly**. Prefer |
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setting compression levels unless there's a _very_ compelling reason to choose |
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specific algorithms (benchmarking, testing). |
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|
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Selection of concrete compression algorithms is performed by adding a |
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`(GRPC_COMPRESS_REQUEST_ALGORITHM_KEY, <algorithm-name>)` key-value pair to the |
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initial metadata, where `GRPC_COMPRESS_REQUEST_ALGORITHM_KEY` is defined in |
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[`grpc/impl/codegen/compression_types.h`](https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h)), |
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and `<algorithm-name>` is the human readable name of the algorithm as given in |
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[the HTTP2 spec](https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md) |
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for `Message-Encoding` (e.g. gzip, identity, etc.). See |
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[`grpc_compression_algorithm_name`](https://github.com/grpc/grpc/blob/master/src/core/lib/compression/compression.c) |
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for the mapping between the `grpc_compression_algorithm` enum values and their |
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textual representation. |
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|
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## Per Message Settings |
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|
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To disable compression for a specific message, the `flags` field of `grpc_op` |
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instances of type `GRPC_OP_SEND_MESSAGE` must have its `GRPC_WRITE_NO_COMPRESS` |
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bit set. Refer to |
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[`grpc/impl/codegen/compression_types.h`](https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h)), |
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|
After Width: | Height: | Size: 89 KiB |
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After Width: | Height: | Size: 120 KiB |
@ -0,0 +1,130 @@ |
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%YAML 1.2 |
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--- | |
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# GRPC CocoaPods podspec |
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# This file has been automatically generated from a template file. |
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# Please look at the templates directory instead. |
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# This file can be regenerated from the template by running |
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# tools/buildgen/generate_projects.sh |
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|
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# Copyright 2015, Google Inc. |
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# All rights reserved. |
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# |
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# Redistribution and use in source and binary forms, with or without |
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# modification, are permitted provided that the following conditions are |
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# met: |
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# |
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# * Redistributions of source code must retain the above copyright |
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# notice, this list of conditions and the following disclaimer. |
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# * Redistributions in binary form must reproduce the above |
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# copyright notice, this list of conditions and the following disclaimer |
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# in the documentation and/or other materials provided with the |
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# distribution. |
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# * Neither the name of Google Inc. nor the names of its |
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# contributors may be used to endorse or promote products derived from |
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# this software without specific prior written permission. |
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# |
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
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# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
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# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
||||
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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|
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<%! |
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def grpc_files(libs): |
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out = [] |
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for lib in libs: |
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if lib.name in ("grpc", "gpr"): |
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out += lib.get('headers', []) |
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out += lib.get('public_headers', []) |
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out += lib.get('src', []) |
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return out; |
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|
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def grpc_private_headers(libs): |
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out = [] |
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for lib in libs: |
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if lib.name in ("grpc", "gpr"): |
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out += lib.get('headers', []) |
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return out |
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%> |
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Pod::Spec.new do |s| |
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s.name = 'gRPC' |
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version = '0.14.0' |
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s.version = version |
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s.summary = 'gRPC client library for iOS/OSX' |
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s.homepage = 'http://www.grpc.io' |
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s.license = 'New BSD' |
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s.authors = { 'The gRPC contributors' => 'grpc-packages@google.com' } |
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|
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s.source = { :git => 'https://github.com/grpc/grpc.git', |
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:tag => "release-#{version.gsub(/\./, '_')}-objectivec-#{version}", |
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:submodules => true } |
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|
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|
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s.ios.deployment_target = '7.1' |
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s.osx.deployment_target = '10.9' |
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s.requires_arc = true |
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|
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objc_dir = 'src/objective-c' |
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|
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# Reactive Extensions library for iOS. |
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s.subspec 'RxLibrary' do |ss| |
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src_dir = "#{objc_dir}/RxLibrary" |
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ss.source_files = "#{src_dir}/*.{h,m}", "#{src_dir}/**/*.{h,m}" |
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ss.private_header_files = "#{src_dir}/private/*.h" |
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ss.header_mappings_dir = "#{objc_dir}" |
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end |
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|
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# Core cross-platform gRPC library, written in C. |
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s.subspec 'C-Core' do |ss| |
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ss.source_files = ${(',\n' + 22*' ').join('\'%s\'' % f for f in grpc_files(libs))} |
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|
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ss.private_header_files = ${(',\n' + 30*' ').join('\'%s\'' % f for f in grpc_private_headers(libs))} |
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|
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ss.header_mappings_dir = '.' |
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# This isn't officially supported in Cocoapods. We've asked for an alternative: |
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# https://github.com/CocoaPods/CocoaPods/issues/4386 |
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ss.xcconfig = { |
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'USE_HEADERMAP' => 'NO', |
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'ALWAYS_SEARCH_USER_PATHS' => 'NO', |
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'USER_HEADER_SEARCH_PATHS' => '"$(PODS_ROOT)/Headers/Private/gRPC"', |
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'HEADER_SEARCH_PATHS' => '"$(PODS_ROOT)/Headers/Private/gRPC/include"' |
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} |
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|
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ss.requires_arc = false |
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ss.libraries = 'z' |
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ss.dependency 'BoringSSL', '~> 3.0' |
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|
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# ss.compiler_flags = '-GCC_WARN_INHIBIT_ALL_WARNINGS', '-w' |
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end |
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|
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# Objective-C wrapper around the core gRPC library. |
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s.subspec 'GRPCClient' do |ss| |
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src_dir = "#{objc_dir}/GRPCClient" |
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ss.source_files = "#{src_dir}/*.{h,m}", "#{src_dir}/**/*.{h,m}" |
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ss.private_header_files = "#{src_dir}/private/*.h" |
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ss.header_mappings_dir = "#{objc_dir}" |
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|
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ss.dependency 'gRPC/C-Core' |
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ss.dependency 'gRPC/RxLibrary' |
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|
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# Certificates, to be able to establish TLS connections: |
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ss.resource_bundles = { 'gRPCCertificates' => ['etc/roots.pem'] } |
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end |
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|
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# RPC library for ProtocolBuffers, based on gRPC |
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s.subspec 'ProtoRPC' do |ss| |
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src_dir = "#{objc_dir}/ProtoRPC" |
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ss.source_files = "#{src_dir}/*.{h,m}" |
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ss.header_mappings_dir = "#{objc_dir}" |
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|
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ss.dependency 'gRPC/GRPCClient' |
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ss.dependency 'gRPC/RxLibrary' |
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ss.dependency 'Protobuf', '~> 3.0.0-alpha-4' |
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end |
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end |
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