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terraform/website/docs/configuration/functions/filesha256.html.md

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lang: New file-hashing functions In prior versions, we recommended using hash functions in conjunction with the file function as an idiom for detecting changes to upstream blobs without fetching and comparing the whole blob. That approach relied on us being able to return raw binary data from file(...). Since Terraform strings pass through intermediate representations that are not binary-safe (e.g. the JSON state), there was a risk of string corruption in prior versions which we have avoided for 0.12 by requiring that file(...) be used only with UTF-8 text files. The specific case of returning a string and immediately passing it into another function was not actually subject to that corruption risk, since the HIL interpreter would just pass the string through verbatim, but this is still now forbidden as a result of the stricter handling of file(...). To avoid breaking these use-cases, here we introduce variants of the hash functions a with "file" prefix that take a filename for a disk file to hash rather than hashing the given string directly. The configuration upgrade tool also now includes a rule to detect the documented idiom and rewrite it into a single function call for one of these new functions. This does cause a bit of function sprawl, but that seems preferable to introducing more complex rules for when file(...) can and cannot read binary files, making the behavior of these various functions easier to understand in isolation.
2019-01-25 18:16:43 +01:00
---
layout: "functions"
page_title: "filesha256 - Functions - Configuration Language"
sidebar_current: "docs-funcs-crypto-filesha256"
description: |-
The filesha256 function computes the SHA256 hash of the contents of
a given file and encodes it as hex.
---
# `filesha256` Function
website: Version notes: Add new -> old links to 0.12 language docs (function pages)
2019-01-17 01:33:57 +01:00
-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
earlier, see
[0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
lang: New file-hashing functions In prior versions, we recommended using hash functions in conjunction with the file function as an idiom for detecting changes to upstream blobs without fetching and comparing the whole blob. That approach relied on us being able to return raw binary data from file(...). Since Terraform strings pass through intermediate representations that are not binary-safe (e.g. the JSON state), there was a risk of string corruption in prior versions which we have avoided for 0.12 by requiring that file(...) be used only with UTF-8 text files. The specific case of returning a string and immediately passing it into another function was not actually subject to that corruption risk, since the HIL interpreter would just pass the string through verbatim, but this is still now forbidden as a result of the stricter handling of file(...). To avoid breaking these use-cases, here we introduce variants of the hash functions a with "file" prefix that take a filename for a disk file to hash rather than hashing the given string directly. The configuration upgrade tool also now includes a rule to detect the documented idiom and rewrite it into a single function call for one of these new functions. This does cause a bit of function sprawl, but that seems preferable to introducing more complex rules for when file(...) can and cannot read binary files, making the behavior of these various functions easier to understand in isolation.
2019-01-25 18:16:43 +01:00
`filesha256` is a variant of [`sha256`](./sha256.html)
that hashes the contents of a given file rather than a literal string.
This is similar to `sha256(file(filename))`, but
because [`file`](./file.html) accepts only UTF-8 text it cannot be used to
create hashes for binary files.