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+# BoringSSL Style Guide
+
+BoringSSL usually follows the
+[Google C++ style guide](https://google-styleguide.googlecode.com/svn/trunk/cppguide.html).
+The rest of this document describes differences and clarifications on
+top of the base guide.
+
+
+## Legacy code
+
+As a derivative of OpenSSL, BoringSSL contains a lot of legacy code that
+does not follow this style guide. Particularly where public API is
+concerned, balance consistency within a module with the benefits of a
+given rule. Module-wide deviations on naming should be respected while
+integer and return value conventions take precedence over consistency.
+
+Some modules have seen few changes, so they still retain the original
+indentation style for now. When editing these, try to retain the
+original style. For Emacs, `doc/c-indentation.el` from OpenSSL may be
+helpful in this.
+
+
+## Language
+
+The majority of the project is in C, so C++-specific rules in the
+Google style guide do not apply. Support for C99 features depends on
+our target platforms. Typically, Chromium's target MSVC is the most
+restrictive.
+
+Variable declarations in the middle of a function are allowed.
+
+Comments should be `/* C-style */` for consistency.
+
+When declaration pointer types, `*` should be placed next to the variable
+name, not the type. So
+
+    uint8_t *ptr;
+
+not
+
+    uint8_t* ptr;
+
+Rather than `malloc()` and `free()`, use the wrappers `OPENSSL_malloc()`
+and `OPENSSL_free()`. Use the standard C `assert()` function freely.
+
+For new constants, prefer enums when the values are sequential and typed
+constants for flags. If adding values to an existing set of `#define`s,
+continue with `#define`.
+
+
+## Formatting
+
+Single-statement blocks are not allowed. All conditions and loops must
+use braces:
+
+    if (foo) {
+      do_something();
+    }
+
+not
+
+    if (foo)
+      do_something();
+
+
+## Integers
+
+Prefer using explicitly-sized integers where appropriate rather than
+generic C ones. For instance, to represent a byte, use `uint8_t`, not
+`unsigned char`. Likewise, represent a two-byte field as `uint16_t`, not
+`unsigned short`.
+
+Sizes are represented as `size_t`.
+
+Within a struct that is retained across the lifetime of an SSL
+connection, if bounds of a size are known and it's easy, use a smaller
+integer type like `uint8_t`. This is a "free" connection footprint
+optimization for servers. Don't make code significantly more complex for
+it, and do still check the bounds when passing in and out of the
+struct. This narrowing should not propagate to local variables and
+function parameters.
+
+When doing arithmetic, account for overflow conditions.
+
+Except with platform APIs, do not use `ssize_t`. MSVC lacks it, and
+prefer out-of-band error signaling for `size_t` (see Return values).
+
+
+## Naming
+
+Follow Google naming conventions in C++ files. In C files, use the
+following naming conventions for consistency with existing OpenSSL and C
+styles:
+
+Define structs with typedef named `TYPE_NAME`. The corresponding struct
+should be named `struct type_name_st`.
+
+Name public functions as `MODULE_function_name`, unless the module
+already uses a different naming scheme for legacy reasons. The module
+name should be a type name if the function is a method of a particular
+type.
+
+Some types are allocated within the library while others are initialized
+into a struct allocated by the caller, often on the stack. Name these
+functions `TYPE_NAME_new`/`TYPE_NAME_free` and
+`TYPE_NAME_init`/`TYPE_NAME_cleanup`, respectively. All `TYPE_NAME_free`
+functions must do nothing on `NULL` input.
+
+If a variable is the length of a pointer value, it has the suffix
+`_len`. An output parameter is named `out` or has an `out_` prefix. For
+instance, For instance:
+
+    uint8_t *out,
+    size_t *out_len,
+    const uint8_t *in,
+    size_t in_len,
+
+Name public headers like `include/openssl/evp.h` with header guards like
+`OPENSSL_HEADER_EVP_H`. Name internal headers like
+`crypto/ec/internal.h` with header guards like
+`OPENSSL_HEADER_EC_INTERNAL_H`.
+
+Name enums like `enum unix_hacker_t`. For instance:
+
+    enum should_free_handshake_buffer_t {
+      free_handshake_buffer,
+      dont_free_handshake_buffer,
+    };
+
+
+## Return values
+
+As even `malloc` may fail in BoringSSL, the vast majority of functions
+will have a failure case. Functions should return `int` with one on
+success and zero on error. Do not overload the return value to both
+signal success/failure and output an integer. For example:
+
+    OPENSSL_EXPORT int CBS_get_u16(CBS *cbs, uint16_t *out);
+
+If a function needs more than a true/false result code, define an enum
+rather than arbitrarily assigning meaning to int values.
+
+If a function outputs a pointer to an object on success and there are no
+other outputs, return the pointer directly and `NULL` on error.
+
+
+## Parameters
+
+Where not constrained by legacy code, parameter order should be:
+
+1. context parameters
+2. output parameters
+3. input parameters
+
+For example,
+
+    /* CBB_add_asn sets |*out_contents| to a |CBB| into which the contents of an
+     * ASN.1 object can be written. The |tag| argument will be used as the tag for
+     * the object. It returns one on success or zero on error. */
+    OPENSSL_EXPORT int CBB_add_asn1(CBB *cbb, CBB *out_contents, uint8_t tag);
+
+
+## Documentation
+
+All public symbols must have a documentation comment in their header
+file. The style is based on that of Go. The first sentence begins with
+the symbol name, optionally prefixed with "A" or "An". Apart from the
+initial mention of symbol, references to other symbols or parameter
+names should be surrounded by |pipes|.
+
+Documentation should be concise but completely describe the exposed
+behavior of the function. Pay special note to success/failure behaviors
+and caller obligations on object lifetimes. If this sacrifices
+conciseness, consider simplifying the function's behavior.
+
+    /* EVP_DigestVerifyUpdate appends |len| bytes from |data| to the data which
+     * will be verified by |EVP_DigestVerifyFinal|. It returns one on success and
+     * zero otherwise. */
+    OPENSSL_EXPORT int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *data,
+                                              size_t len);
+
+Explicitly mention any surprising edge cases or deviations from common
+return value patterns in legacy functions.
+
+    /* RSA_private_encrypt encrypts |flen| bytes from |from| with the private key in
+     * |rsa| and writes the encrypted data to |to|. The |to| buffer must have at
+     * least |RSA_size| bytes of space. It returns the number of bytes written, or
+     * -1 on error. The |padding| argument must be one of the |RSA_*_PADDING|
+     * values. If in doubt, |RSA_PKCS1_PADDING| is the most common.
+     *
+     * WARNING: this function is dangerous because it breaks the usual return value
+     * convention. Use |RSA_sign_raw| instead. */
+    OPENSSL_EXPORT int RSA_private_encrypt(int flen, const uint8_t *from,
+                                           uint8_t *to, RSA *rsa, int padding);
+
+Document private functions in their `internal.h` header or, if static,
+where defined.