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83 lines
3.3 KiB
Go
83 lines
3.3 KiB
Go
/*
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Maddy Mail Server - Composable all-in-one email server.
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Copyright © 2019-2020 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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package module
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import (
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"context"
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"github.com/emersion/go-message/textproto"
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"github.com/foxcpp/maddy/framework/buffer"
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)
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// Modifier is the module interface for modules that can mutate the
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// processed message or its meta-data.
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//
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// Currently, the message body can't be mutated for efficiency and
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// correctness reasons: It would require "rebuffering" (see buffer.Buffer doc),
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// can invalidate assertions made on the body contents before modification and
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// will break DKIM signatures.
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//
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// Only message header can be modified. Furthermore, it is highly discouraged for
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// modifiers to remove or change existing fields to prevent issues outlined
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// above.
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//
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// Calls on ModifierState are always strictly ordered.
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// RewriteRcpt is newer called before RewriteSender and RewriteBody is never called
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// before RewriteRcpts. This allows modificator code to save values
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// passed to previous calls for use in later operations.
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//
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// Modules implementing this interface should be registered with "modify." prefix in name.
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type Modifier interface {
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// ModStateForMsg initializes modifier "internal" state
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// required for processing of the message.
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ModStateForMsg(ctx context.Context, msgMeta *MsgMetadata) (ModifierState, error)
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}
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type ModifierState interface {
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// RewriteSender allows modifier to replace MAIL FROM value.
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// If no changes are required, this method returns its
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// argument, otherwise it returns a new value.
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//
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// Note that per-source/per-destination modifiers are executed
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// after routing decision is made so changed value will have no
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// effect on it.
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//
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// Also note that MsgMeta.OriginalFrom will still contain the original value
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// for purposes of tracing. It should not be modified by this method.
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RewriteSender(ctx context.Context, mailFrom string) (string, error)
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// RewriteRcpt replaces RCPT TO value.
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// If no changed are required, this method returns its argument, otherwise
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// it returns a new value.
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//
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// MsgPipeline will take of populating MsgMeta.OriginalRcpts. RewriteRcpt
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// doesn't do it.
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RewriteRcpt(ctx context.Context, rcptTo string) (string, error)
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// RewriteBody modifies passed Header argument and may optionally
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// inspect the passed body buffer to make a decision on new header field values.
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//
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// There is no way to modify the body and RewriteBody should avoid
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// removing existing header fields and changing their values.
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RewriteBody(ctx context.Context, h *textproto.Header, body buffer.Buffer) error
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// Close is called after the message processing ends, even if any of the
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// Rewrite* functions return an error.
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Close() error
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}
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