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127 lines
4.6 KiB
Markdown
127 lines
4.6 KiB
Markdown
# LibCurl Sandbox
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This library is a sandboxed version of curl's C API,
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[libcurl](https://curl.haxx.se/libcurl/c/), implemented using Sandboxed API.
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## Setup
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The repository can be cloned using: `git clone --recursive <URL to this repo>`
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The `--recursive` flag ensures that submodules are also cloned.
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Alternatively, if the repository has already been cloned but the submodules have
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not, these can be cloned using: `git submodule update --init --recursive`
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The full list of Sandboxed API dependencies can be found on
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[Sandboxed API Getting Started page](https://developers.google.com/code-sandboxing/sandboxed-api/getting-started).
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The following commands, used from the current `curl/` directory, build the
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library:
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```bash
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mkdir -p build && cd build
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cmake .. -G Ninja -D SAPI_ROOT=<path to sandboxed-api>
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cmake --build .
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```
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## Implementation details
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All of libcurl's methods are supported by the library. However, a few of these
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have different signatures defined in the sandboxed header `custom_curl.h`, which
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wraps and extends libcurl.
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This is necessary because Sandboxed API sandboxes most of libcurl correctly, but
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encounters some issues when sandboxing a few methods. The simplest solution is
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wrapping these methods into wrapper methods that accomplish the same tasks but
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can also be sandboxed.
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The next sections describe the issues encountered and contain some information
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on the signatures of the wrapper methods solving these issues.
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#### Variadic methods
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Variadic methods are currently not supported by Sandboxed API. To solve this,
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these methods are defined with an additional explicit parameter in
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`custom_curl.h`.
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The methods are:
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- `curl_easy_setopt`. Use `curl_easy_setopt_ptr`, `curl_easy_setopt_long` or
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`curl_easy_setopt_curl_off_t` instead.
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- `curl_easy_getinfo`. Use `curl_easy_getinfo_ptr` instead.
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- `curl_multi_setopt`. Use `curl_multi_setopt_ptr`, `curl_multi_setopt_long`
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or `curl_multi_setopt_curl_off_t` instead.
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- `curl_share_setopt`. Use `curl_share_setopt_ptr` or `curl_share_setopt_long`
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instead
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#### Methods with incomplete array arguments
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Incomplete array arguments are currently not supported by Sandboxed API. To
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solve this, methods taking an incomplete array argument have a wrapper in
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`custom_curl.h`, and take a pointer as the argument.
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The methods are:
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- `curl_multi_poll`. Use `curl_multi_poll_sapi` instead.
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- `curl_multi_wait`. Use `curl_multi_wait_sapi` instead.
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#### Methods with conflicts on the generated header
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Some methods create conflicts on the generated header because of redefined
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`#define` directives from files included by the header. To solve this, the
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conflicting types and methods are redefined in `custom_curl.h`.
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The types are:
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- `time_t`. Use `time_t_sapi` instead.
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- `fd_set`. Use `fd_set_sapi` instead.
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The methods are:
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- `curl_getdate`. Use `curl_getdate_sapi` instead.
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- `curl_multi_fdset`. Use `curl_multi_fdset_sapi` instead.
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#### Function pointers
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The functions whose pointers will be passed to the library's methods
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(*callbacks*) can't be implemented in the files making use of the library, but
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must be in other files. These files must be compiled together with the library,
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and this is done by adding their absolute path to the cmake variable
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`CURL_SAPI_CALLBACKS`.
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The pointers can then be obtained using an `RPCChannel` object, as shown in
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`example2.cc`.
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## Examples
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The `examples` directory contains the sandboxed versions of example source codes
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taken from [this page](https://curl.haxx.se/libcurl/c/example.html) on curl's
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website. More information about each example can be found in the examples'
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[README](examples/README.md).
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To build these examples when building the library, the cmake variable
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`CURL_SAPI_ENABLE_EXAMPLES` must be set to `ON`. This enables Sandboxed API
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examples as well.
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## Policy
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The `sandbox.h` file contains a policy allowing all is necessary for libcurl to
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perform simple requests. It is used by all the examples, except by example3.
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This example needs some additional policies and files in its namespace (since it
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uses HTTPS), and the file `example3.cc` shows how to easily extend an existing
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policy.
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## Testing
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The `tests` folder contains some test cases created using Google Test. The class
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`CurlTestUtils` is used to facilitate some tasks that all test cases need,
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including the setup of a mock local server on which test requests are performed.
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To build these tests when building the library, the cmake variable
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`CURL_SAPI_ENABLE_TESTS` must be set to `ON`. This enables Sandboxed API tests
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as well.
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## Callbacks
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The `callbacks.h` and `callbacks.cc` files implement all the callbacks used by
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examples and tests.
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